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Applications of 2DIR on Solution Dynamics and Reaction Chemistry

ProQuest Dissertations and Theses, 2011
Dissertation
Author: Robert W McCanne
Abstract:
Two-dimensional infrared (2DIR) spectroscopy provides a powerful framework with which to study equilibrium solvation dynamics and non-equilibrium reaction solvation by directly providing the frequency-frequency correlation function. Here the Fourier Transform-2DIR method is extended to non-equilibrium reactions by implementing Pump-Probe-2DIR, which provides the frequency correlation of the resulting photoproduct. Home-built infrared and visible light sources enabled the implementation of these novel experimental methods. The non-equilibrium photocleavage of tungsten hexacarbonyl was studied. The photoproduct was found to be vibrationally hot, resulting in transitions observed from the first excited manifold to the second manifold and ground state The 2D spectrum allowed an unambiguous photoproduct peak assignment. The rotational reorientation time was found to depend on visible-pump/2DIR-probe delay, relaxing in at most 60 ps. Moreover, an additional peak was found that explicitly requires intramolecular vibrational energy redistribution (IVR) during the 2DIR waiting time. The IVR was found to slow from ∼200 fs to ∼2 ps as the pump-probe delay increased, consistent with calculations of the bath phonon density of states evaluated at the vibrational energy difference of the two states involved in IVR. The equilibrium solvation dynamics of triruthenium dodecacarbonyl [Ru 3 (CO)12 ] was studied. Significantly faster IVR and spectral diffusion were observed relative to other metal carbonyls studied in the laboratory. Spectral diffusion was also observed in relatively weakly interacting solvents n-hexane and cyclohexane, which has not been observed for other metal carbonyls. This was attributed to detecting not the sampling of microscopic solvent environments per se, but instead sampling a loose conformational space of the flexible Ru 3 (CO)12 molecule. For the case of polar, hydrogen bonding solvents, calculations indicate an increase in solvent disorder causes an increase in carbonyl participation ratio, indicative of increased delocalization. This unusual observation was attributed to the odd-membered ring symmetry of the metal center, which results in frozen, frustrated carbonyl motions. Together, unfreezing of carbonyl motions and faster IVR and spectral diffusion times were taken to indicate that Ru 3 (CO)12 has a relatively loose solvated equilibrium structure. Calculations of the potential minimum confirm that multiple conformations lie at nearly equivalent energies, with the highly symmetric strained structure partially stabilized by "carbon bonds."

Table of Contents List of Figures v List of Tables vm Chapter 1 Introduction 1 1 1 Dynamics 1 111 Timescales and motions 1 1 1 2 Non-equilibrium motion 2 1 1 3 Adapting to the ultrafast 4 1 2 Linear spectroscopy limitations 5 1 3 Non-linear spectroscopy 7 1 3 1 Transient absorption spectroscopy 7 1 3 2 Multidimensional spectroscopy 8 Chapter 2 Theoretical Framework and Background 16 2 1 The Optical Response Function 16 2 11 General optical response 16 2 12 Linear spectroscopy 20 2 13 Third-order Spectroscopy 22 2 2 Liouville pathways 23 2 3 Excitons 33 2 3 1 General electronic exciton models 33 2 3 2 Light Harvesting and the Fenna-Matthews-Olson Complex 34 2 3 3 J Aggregates 35 2 4 VibrationaP'excitons" 36 Chapter 3 Experimental Methods 40 3 1 Generation of 2DIR 40 u

3 1 1 OPA 40 3 1 2 DFG 43 3 13 Interferometer 44 3 14 Two-dimensional spectra 46 3 1 5 FT-2DIR vs double resonance 2DIR 46 3 2 Upconversion 49 3 3 Transient spectroscopy 52 3 3 1 Narrowband excitation 52 3 3 2 Broadband generation and excitations 54 3 3 3 Flowing sample 60 3 3 4 Transient 2DIR 63 Chapter 4 A Transient 2DIR Examination of Tungsten Hexacarbonyl 69 4 1 Design and testing using dimanganese decacarbonyl 69 4 2 Transient 2DIR of tungsten hexacarbonyl 75 4 2 1 Experimental concerns 75 4 2 2 W(CO)6 results 77 4 2 3 Discussion of transient W(CO)6 spectroscopy and hot photoproducts 83 4 3 Conclusions 85 Chapter 5 Vibrational Energy Transfer and Spectral Diffusion Dynamics in a Vibrational Aggregate with Disorder-Induced Derealization 88 5 1 Introduction 88 5 11 Dynamics 88 5 12 Spectral Diffusion and Intermolecular Vibrational Energy Redistribution 90 5 13 Excitomc Modeling 93 5 2 Expenmental and Modeling Methods 94 5 3 Results 98 in

5 3 1 Experimental 5 3 2 Modeling 104 5 4 Discussion 110 5 5 Conclusion 113 Chapter 6 Conclusions 117 6 1 Experimental transient 2DIR 117 6 2 Transient W(CO)6 and additional information content 118 6 3 Equilibrium Ru3(CO)i2 and disorder-induced delocalization 119 6 4 Outlook 121 IV

List of Figures Figure 1 (a) Non-equihbnum, (b) equilibnum dynamics of solvated metal carbonyls 2 Figure 2 Progression from linear to transient multidimensional spectr 6 Figure 3 Time ordering of light-matter field interactions field-free evolution 19 Figure 4 Matenal linear interaction with an applied light field 21 Figure 5 Material interaction to the third order of an electric field 22 Figure 6 Illustration ofrephasing and non-rephasing propagation 24 Figure 7 Energy level versus double sided Feynman diagram 25 Figure 8 Set of six double-sided Feynman diagrams for FWM 26 Figure 9 Additional pathways beyond rephasing and non-rephasing 28 Figure 10 Energy matching between the system and bath energy levels 29 Figure 11 Peak growth with waiting time due to IVR is analogous to exchange 29 Figure 12 Spectral diffusion produces a signature tilt at early waiting times 30 Figure 13 Juxtaposition of a harmonic potential and a Morse potential 31 Figure 14 Ground and excited electronic energy surfaces with a transition between 32 Figure 15 Calculation of the transition dipole moments of the FMO complex 34 Figure 16 Aggregation of cyanine dipole into quasi-one-dimensional J-aggregate 36 Figure 17 Cyanine vibrational frequency shift with aggregation 36 Figure 18 Schematic for converting 800 nm titanium sapphire laser output to the IR 41 Figure 19 Pulse diagram for Founer transform 2DIR (a) equilibnum expenments and (b), (c) non-equihbnum expenments 44 Figure 20 (a) Founer transform 2DIR pulse generation schematic from DFG on as compared to (b) Double resonance pulse generation method 47 Figure 21 Upconversion of signal and local oscillator fields by sum frequency addition to a highly stretched chirped pulse 49 v

Figure 22 (a) Optimum phase matchmg angle for two incoming fields with separation angle a in the BBO crystal 53 Figure 23 Schematic of the NOPA implementation 55 Figure 24 NOPA compression process 58 Figure 25 Companson of (a) negatively chirped NOPA output without deformable mirror compression and (b) near transform limited NOPA 60 Figure 26 Diagram of the wire-guided jet and flowing cell 61 Figure 27 The excitation field is chopped at half the laser repetition rate 65 Figure 28 UV/Vis reaction pathway for the dissociation of DMDC 70 Figure 29 Excitation at lower energies produces overlapped transient spectra 71 Figure 30 Higher energy excitation preferentially cleaves a carbonyl 72 Figure 31 Transient 2DIR of DMDC excited by 400 nm light 73 Figure 32 A scan of tz and T produces a large set of PP-2DIR spectra 74 Figure 33 Excitation of tungsten hexacarbonyl in the near UV results in metal-carbon bond cleavage, producing the pentacarbonyl and free CO 75 Figure 34 W(CO)e transients are well separated from the parent bleach 76 Figure 35 PP-2DIR spectra of W(CO)e varying waiting time and pump-probe delay 78 Figure 36 Peak assignments for the transient diagonal and cross peaks 79 Figure 37 Hexacarbonyl parent and pentacarbonyl product energy levels 80 Figure 38 Crosspeak between 1942 and 1928 cm"1 requires IVR 80 Figure 39 Peak volume as a function of waiting time for Dew peak (1927 cm"1) 81 Figure 40 Decrease in reonentational rate with greater pump-probe delay 82 Figure 41 Peak volume as a function of waiting time at early times 82 Figure 42 Peak maximum waiting time as a function of pump-probe delay 83 Figure 43 Two vibrational modes of Ru3(CO)i2 as calculated by DFT 90 Figure 44 Representative Feynman diagrams showing the excitation orders resulting in VI

the t2 behavior of interest 91 Figure 45 Representative t2 spectra of Ru3(CO) n 99 Figure 46 (a) The inhomogeneity ratio of peak 5 as a function of waiting time for three solvents n-hexane, hexanol, and butanol with their corresponding fits 101 Figure 47 Companson of the inhomogeneity ratio of peaks 1,5, and 9 in the same solvent 102 Figure 48 (a), (b) Companson of the eigenvector found by Hamiltonian generation to the DFT calculated amplitudes of carbonyl motion for modes 10 and 11 respectively 105 Figure 49 (a) Calculated linear spectrum as a function of disorder as compared to (b) expenmental linear spectrum for a range of solvents 107 Figure 50 Shift with disorder of IR-active modes 108 Figure 51 Shift with disorder of Raman modes 109 Figure 52 Calculated spectrum for (a) 2 cm"1 and (b) 12 cm"1 of broadening 109 Figure 53 Reported products following photodissociation of Ru3(CO)i2 122 vn

List of Tables Table 1 IVR Time Constants (in ps) 103 Table 2 Spectral Diffusion Time Constants (m ps) 104 Table 3 Optimized Vibrational Exciton Hamiltoman Parameters 106 vin

Chapter 1 Introduction 1.1: Dynamics 1.1.1 Timescales and motions Nearly all reaction chemistry occurs in solution16 Particulate interaction simply occurs much more readily and frequently in condensed phases as compared to the gas phase, and liquids in particular provide sufficient freedom of motion allowing diffusion and collision as compared to the rigidity of solids6 The solution itself also plays a stabilizing role for intermediates necessary for reactions to occur7 This makes the solution phase ideal for both the initial approach and eventual collision resulting in a chemical reaction5 Thus understanding solvation dynamics across a range of timescales is vital m understanding and controlling reactions and reactivity8 These microscopic interactions govern the energetics and the timescales of solution chemistry, and must be probed from both the solute and solvent perspective9 The processes that underlie chemical and reaction dynamics include motional and energetic fluctuations of both the solvent and solute as the two components adjust to being in solution 10U Equilibrium flucutations1 lead to processes ranging from simple energy level fluctuations in both the solute and solvent on a sub-picosecond timescale, to more complicated equilibrium spectral diffusion and isomerization on a few picosecond timescale, to very complex non-equihbnum reactions propagation along a diverging energy coordinate on a hundreds of picoseconds timescale8 These fast motions then lead to complex reaction on 1

solvent 2,000 °C R/ Figure I (a) Non-equihbnum, (b) equilibrium dynamics ofsolvated metal carbonyls microsecond to many second timescales n We have considered some aspects of solvation and reaction dynamics by studying in detail metal carbonyl system W(CO)6 and Ru3(CO)i2that allow tractable treatment both experimentally and using simple models While important in catalytic and CO reaction chemistry, these systems also provide an important step towards fully characterizing complex ultrafast dynamics 13>14 112 Non-equilibrium motion Energy harnessing and transport depends on a host of properties 15'20 Not only does the equilibrium structure play an important role in the efficiency and speed of charge transfer, but in many energy applications propagation of the electron from absorption to conduction causes non-equilibrium distortions, resulting in stress to the well ordered solid structure21 Such distortions occur rapidly very locally but are dispersed temporally along the path traveled by the electron, requmng monitoring and analysis on a range of timescales22 These stresses are one of the primary factors in lithium-ion battery breakdown over repeated charge and discharge cycles23 A clear understanding of the intermolecular interactions, both electronic and vibrational, may lead to methods to better suppress such destructive motions23 This in turn would produce more stable long term energy capture and storage matenals23 2

The Born-Oppenheimer approximation is highly successful due to the large separation of masses between the electrons and the nuclei, and neatly divides chemical calculations into two regimes that can be computed dependently but separately 24~26 Clearly, however, when non-equilibnum conditions are excited, as in a photoreaction, electronic changes will induce atomic motions due to the same separation27 In this way, the approximation can break down, and coupled vibronic states must be considered24-27 Though the analogy used here involves induced vibrational movements after a reaction, indeed any time two electronic states are separated by energies similar to the separation of vibrational energies, electronic and vibrational coordinates will mix and vibronic coupling becomes importantM Mixing was demonstrated experimentally as early as the 1930s with an excited Ji-state of CO228 Shortly thereafter calculations predicted the benzene spectrum and indicated the prevalence of vibronically mixed states29 Both understanding and exploiting the coupling of motions continues to be an active area of research30-31 Often, rearrangements and reactions are dnven along specific coordinates that couple strongly to faster timescale motions, in opposition to the electronically dnven vibrations presented above3032 In the case of azobenzene, two isomeric states exist, cis and trans, the reaction between which occurs via excitation with near-UV energy33 Previous work has focused on specific internal motions, such as the out of plane rocking motion of the benzene rings, and their relationship to this isomenzation34 It has been suggested that sufficient vibrational energy deposited into this motion via the infrared could couple to the otherwise higher UV-energy isomenzation transition, exciting the trans to cis movement vibrationally instead of electronically33 Expenments have hinted at this coupling, though it remains difficult to fully map on a multidimensional vibrational landscape34 Isomenzation is often reduced to single coordinate "isomenzation angle" where many degrees of freedom are collected into a single expenmental parameter, here the out of plane rocking motion35 In contrast, other theones have suggested an in plane inversion occurs wherein one nitrogen undergoes an umbrella-like inversion in the symmetry plane36 The energy landscape is not a simplified one dimensional with a single energy 3

barrier, but a multidimensional surface with many-dimensional hills37 Traversing the hill corresponds to excitation over the barrier to the product, but there are additional paths that instead skirt around the barrier, using the additional degrees of freedom to bypass traditional transition states37 These may be the paths taken in the absence of artificial excitation, relying instead on probabilistic absorption of available kBT energy37 The in- plane inversion of azobenzene is one possible path that bypasses isomenzation via twisting Understanding vibromc coupling in larger systems require new methods of spectroscopy to fully monitor motions that occur during reaction, including a method of mapping reactants to products38 1.13 Adapting to the ultrafast Reactants evolve on ultrafast timescales, in the picosecond and even femtosecond regime, where initial electron redistribution dnves nuclear motions25 While NMR has developed many tools and complex pulsing methods to access additional dynamics, it is nevertheless ultimately limited39 Because NMR uses radio frequencies the temporal resolution is limited to timescales on the order of the penod, or around 1 ns5 Electromagnetic radiation cannot be used to effectively probe events smaller than a single cycle of the wavelength without encountenng uncertainty limitations39 New techniques and shorter wavelengths are necessary to access faster dynamics40 Infrared spectra report on the vibrational state of an ensemble of weakly coupled parts of an entire molecule, which can result in many groups of peaks41 Though this is rich in information content, it leads to congested areas where many vibrations, or even local inhomogeneities, cause peaks to overlap42 Visible spectra, on the other hand, probe the total electronic response of a system, often a single or few transitions between a limited set of electronic states43 These whole molecule responses can be difficult to map to nuclear movements, requiring calculation of the entire molecular electron density at any given time pointu Applying the multidimensional techniques adapted from NMR to the infrared allows the molecular response to be teased apart, providing sufficient resolution for analysis 45 4

1.2: Linear spectroscopy limitations Because linear spectroscopy provides time averaged information, any processes faster than the scan length appear as averaged in the resulting spectra8 Peaks are broadened by multiple factors mixed together into a single observable hnewidth39 The lifetime of the states in question provides a starting point for linewidths, where the inverse of the lifetime gives the spectral width of an otherwise isolated transition8 In solution, however, the hnewidth and lifetime are generally uncoupled43 In the infrared, narrow linewidths are achieved m cooled gas phase experiments, where the only additional consideration is Doppler broadening ** In solution this width is only approached in the most non-interacting of solvents43 Particularly in the visible, overlapping transitions and broadened electronic linewidths make extracting dynamics difficult at best43 The extracted dynamics are also electronic in nature, not atomic, requiring modeling to characterize47 In contrast, infrared spectroscopy reports on molecular vibrations, which are extremely highly correlated with small geometry changes48 A bond 1 A long will appreciably change frequency with only a 0 1 A atomic movement8 In this way the infrared spectrum is inherently sensitive to positional information almost directly, though there remains the inevitable need to combine experiment with computation49 In a linear spectrum in solution, sub-angstrom movements caused by sampling many microstates result in frequency fluctuations, producing broadening of the optical absorption line shape50 In some cases, this effect is small, as in isolated vibrations that do not couple to the bath, while in others the effect is much larger51 The OH stretch, for example, is broadened in many liquids over hundreds of wavenumbers, covenng a large region around 3200 cm"1 and overlapping the entire CH stretching region near 3000 cm" 152 Hydrogen bonding dynamics in general prove difficult to extract from linear spectra, as the energy involved is much greater than even other liquid dipoles53 Increased interaction energies between a solute and solvent mean further distortion from the isolated gas phase model for either54 This also increases the complexity when modeling 5

the system, as well55 Ultimately, the larger interaction between solute and solvent blurs Figure 2 Progression from linear to transient multidimensional spectra Linear spectra (a) three transitions are complicated by overlap of three transient features (b) In two dimensions (c), crosspeaks provide additional correlations and complications, which are further enhanced in 2D transient spectra (d) the distinction between the system and surroundings56 Note that in addition to inducing a large number of slightly altered local environments, highly interacting solvents may also change the overall lifetime of an excited state43 Thus there are two effects occumng simultaneously that prove difficult to disentangle Indeed, in some sense the altered microscopic environment can be thought of as an alteration to the lifetime43 This inhomogeneity can be either static or dynamic, and in the latter case observation of the dynamic evolution of spectral inhomogeneity is tantamount to recording ultrafast snapshots of equilibrium solvation 6

1.3: Non-linear spectroscopy Though the frequency and time domain are in principle interchangeable by Founer transformation, multiple dynamical processes hidden inside a single expenmental observable such as hnewidth makes sampling in the time domain preferable in some cases57 As such, it is necessary to define a starting point from which time dependent motions will be sampled to measure the molecular response in the time domain58 These non-linear expenments create a correlation map of molecular energies to elucidate fast solvation effects57 1.3.1 Transient absorption spectroscopy In transient absorption spectroscopy an initial field-matter interaction provides access to a non-equihbnum state from which evolves as a function of time A second field-matter interaction then reports on the evolution at later times This can be done using a pump and probe of many frequencies, including IR, UV/visible, and x-ray59_62 Visible pump, visible probe is employed to study ultrafast reactions through their electronic evolution36 Visible pump, IR probe is also used, providing a picture the vibrations following a photoreaction63 New advances in visible pump, x-ray probe have been reported, leading towards ultrafast transient x-ray expenments X-ray probes produce atomic coordinates directly, but current x-ray pulse durations still he in the hundred picosecond regime M Much work has been done on creating shorter pulses for better time resolution and access to faster dynamics, and could one day give atomic coordinates with sub-femtosecond resolution65 Until then, ultrafast pulses in the visible and IR provide the best trade-off of atomic resolution for temporal resolution Given a pair of pump and probe pulses, the spectrum of a photoinduced process can be monitored with resolution dictated by the pulse temporal widths The result is a senes of spectra of the transient photoproducts as they evolve Photoreactions can be chosen such that the transient evolution mirrors a natural process under study, such as excitation to an electronic state that lacks a barner present in the ground electronic state, 7

leading to isomenzation or dissociation following photolysis49 Probing persistent excited electronic states can be informative by mapping the energy potential landscape of a non- eqmhbnum potential well involved in energy transfer " Vibrational excitation aids m illuminating the full vibrational potential well of a given electronic state67 The same issues of congestion that obscure linear spectra are still present in transient spectra Because transient spectra are the superposition of multiple species, often they are more congested than their linear counterparts68 Differences between spectra with and without excitation are often taken to highlight changes due solely to the photoexcitation The result is a combination of both positive going (transient) peaks due to the formation of non-equilibrium species and negative going (bleach) peaks due to the loss of the equilibrium ground state species Lineshapes are distorted by overlap with opposite sign features In sufficiently resolved spectra characterizing transient peaks can be done by careful fitting to find peak centers and widths69 Additional peaks and broadening in a region can make the problem intractable68 In addition, no information pertaining to the evolution through the transition state is contained in even the transient difference spectra38 Reactants with multiple peaks do not map directly onto corresponding product peaks, instead, product absorptions show only evolution following photoreaction70 Transitions states by then- nature are unstable, sometimes occurring in and persisting for femtoseconds or less8 Probing occurs on a system already electronically perturbed from equilibrium in all but the slowest of transition state formations 71 1.3.2 Multidimensional spectroscopy Building from work using NMR, multiple axes can be employed to exploit additional spectral resolution in the cases of congestion, revealing hidden dynamical information, probing the higher-order response of a system, and illuminating additional features of the molecular energy landscape45 Two-dimensional infrared (2DIR) and multidimensional infrared (MDIR) spectroscopy have emerged as an method of probing the nonlinear dynamics in solution on a picometer scale with sub-picosecond time 8

resolution43 Exploiting this resolution in multiple dimensions provides a sensitive method of probing many equilibrium solution dynamics, with extension to non- equihbnum processes as well43 Frequency information, spread across two axis, provides a very sensitive probe of local solvation homogeneity, while time information along a third axis provides access to femtosecond and picosecond dynamics72 Additionally, while 2DIR probes all of these variables at equilibrium, non-equihbnum reactions can be studied by applying an additional light source and monitoring the resulting products using 2DIR73 This extends all of the advantages of 2DIR to both initial reactant dynamics and the resulting product formation dynamics74 This is of use in cases where one dimensional pump probe experiments produce overlapping features70 Modeling, a key tool in deconvolving congested linear spectra, is more difficult with evolving reacting species I3 Addition of a second axis makes identifying such a case much easier73 Finally, a truly unique type of non-equihbnum 2DIR expenment probes not just the reactant and product states with aforementioned sensitivity, but in fact connects these states over the reaction barrier73 Transition state chemistry is the heart of any reaction, and thus of singular importance in understanding reactions, solution phase or otherwise75 Because of the transient nature, however, the transition state is all but impossible to observe76 One dimensional transient spectroscopy produces a discrete before and after picture but only resolves the early product state41 A 2DIR triggered exchange expenment initializes monitoring before the photoreaction, however, leading to correlation through the transition state38 It can be thought of as labeling the reactant with the initialization of a 2DIR expenment, then applying the photoexcitation, and finally reading out the final product state Detection then correlates initial reactant frequency with detected product frequency While still in the infant stage, this new spectroscopy will aid in understanding reactions in many ways Work by Hamm et al on the metal-to-hgand charge transfer (MLCT) in [Re(CO)3Cl(dmbpy)] (dmbpy = 4,4'-dimethyl-2,2'bipyndine) showed that, contrary to previous believed, the two CO vibrational modes of the product do not correlate directly to the two corresponding product modes38 Instead the CO modes switch frequency 9

ordenng, with the low frequency reactant mode becoming the high frequency product mode, and vice versa There is currently no other experimental method that provides this direct reactant to product frequency mapping It is worth noting, however, that the technique used by Bredenbeck et al lacks the very highest possible time resolution within the 2DIR probe due to their hybrid frequency-time domain approach By employing a narrowband IR pump pulse, there is necessarily a loss of time resolution due to the requirement of separating the pump and probe pulses in time This minimum time delay of between 500-1000 fs implies that rapid intramolecular vibrational redistribution can occur faster than the experiment and will diminish the ability to map product transitions to those on the reactant Indeed, recent unpublished work in our group on the same Re complex indicates that IVR among all three vibrational modes is very rapid (<2ps), suggesting that the hybrid double-resonance-like method of Bredenbeck et al is not well suited for such rapid reactant vibrational dynamics In this thesis work is descnbed that circumvents the technical limitations by demonstrating, for the first time, electronically tnggered, transient Fourier-transform 2DIR spectroscopy 10

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Full document contains 132 pages
Abstract: Two-dimensional infrared (2DIR) spectroscopy provides a powerful framework with which to study equilibrium solvation dynamics and non-equilibrium reaction solvation by directly providing the frequency-frequency correlation function. Here the Fourier Transform-2DIR method is extended to non-equilibrium reactions by implementing Pump-Probe-2DIR, which provides the frequency correlation of the resulting photoproduct. Home-built infrared and visible light sources enabled the implementation of these novel experimental methods. The non-equilibrium photocleavage of tungsten hexacarbonyl was studied. The photoproduct was found to be vibrationally hot, resulting in transitions observed from the first excited manifold to the second manifold and ground state The 2D spectrum allowed an unambiguous photoproduct peak assignment. The rotational reorientation time was found to depend on visible-pump/2DIR-probe delay, relaxing in at most 60 ps. Moreover, an additional peak was found that explicitly requires intramolecular vibrational energy redistribution (IVR) during the 2DIR waiting time. The IVR was found to slow from ∼200 fs to ∼2 ps as the pump-probe delay increased, consistent with calculations of the bath phonon density of states evaluated at the vibrational energy difference of the two states involved in IVR. The equilibrium solvation dynamics of triruthenium dodecacarbonyl [Ru 3 (CO)12 ] was studied. Significantly faster IVR and spectral diffusion were observed relative to other metal carbonyls studied in the laboratory. Spectral diffusion was also observed in relatively weakly interacting solvents n-hexane and cyclohexane, which has not been observed for other metal carbonyls. This was attributed to detecting not the sampling of microscopic solvent environments per se, but instead sampling a loose conformational space of the flexible Ru 3 (CO)12 molecule. For the case of polar, hydrogen bonding solvents, calculations indicate an increase in solvent disorder causes an increase in carbonyl participation ratio, indicative of increased delocalization. This unusual observation was attributed to the odd-membered ring symmetry of the metal center, which results in frozen, frustrated carbonyl motions. Together, unfreezing of carbonyl motions and faster IVR and spectral diffusion times were taken to indicate that Ru 3 (CO)12 has a relatively loose solvated equilibrium structure. Calculations of the potential minimum confirm that multiple conformations lie at nearly equivalent energies, with the highly symmetric strained structure partially stabilized by "carbon bonds."