Energy Relaxation Pathways Research Articles

Vibrational energy relaxation pathways of water

Vibrational energy relaxation (VR) of the OH stretch ν OH and bend δ H 2O in water is studied by the mid-IR pump with anti-Stokes Raman probe technique. The broad ν OH band in water consists of two inhomogeneously broadened subbands. VR in the larger red-shifted subband ν OH R, with T 1=0.55 ps, is shown to occur by the mechanism ν OH→ δ H 2O (1/3) and ν OH → ground state (2/3). VR in the smaller longer-lived blue-shifted subband ν OH B, with T 1=0.75 ps, occurs by the mechanism ν OH → ground state. The bending fundamental δ H 2O decays directly to the ground state with T 1=1.4 ps.

Vibrational energy relaxation rate constants from linear response theory

A new approach for the calculation of vibrational energy relaxation rate constants is introduced. The new approach is based on linear response theory, and is shown to have several distinct advantages over the standard Landau–Teller formula, which is based on the Bloch–Redfield theory, namely: (1) weak system–bath coupling is not assumed; (2) selectivity in choosing the vibrational energy relaxation pathway, including non-Landau–Teller pathways, is possible; (3) the validity of rate kinetics can be explicitly verified; (4) direct extraction of the high-frequency tail of the force–force correlation function is avoided. A detailed analysis of the conditions under which the new expression reduces into the Landau–Teller formula, and an application in the case of bilinear coupling to a harmonic bath are provided.

Two-dimensional vibrational spectroscopy. VIII. Infrared optical Kerr effect and two-color infrared pump–probe measurements

The infrared optical Kerr effect (IR-OKE) and two-color infrared pump–probe spectroscopies, which can be directly used to study intermolecular vibrational energy relaxation pathways, are theoretically studied. The IR-OKE method involves an intense IR pulse with controlled frequency to build up large population on a specific intramolecular vibrationally excited state. After a finite mixing time, which is also experimentally controlled, the time evolution of the nonequilibrium density matrix is detected by using the femtosecond optical Kerr effect measurement. Due to the nonequilibrium population distribution initially induced by the intensive infrared pulse, the measured OKE signal differs from that measured for a molecular system initially in thermal equilibrium state. Particularly, it is found that the deviation from the harmonic response can be specifically measured by using this method. By following the same procedure developed in this paper, the two-color IR pump–probe absorption spectroscopy is also considered and the corresponding nonequilibrium IR response function is theoretically investigated with a direct comparison with complementary IR-OKE response function. By using the perturbation theory, the corresponding response functions are obtained in terms of the molecular properties such as linear and nonlinear spatial derivatives of dipole and polarizability and cubic and quartic anharmonic coefficients. Also, it is emphasized that this method is conceptually quite similar to the transient nuclear Overhauser effect nuclear magnetic resonance spectroscopy.

Transient resonance Raman spectroscopic studies of some paramagnetic metalloporphyrins: effects of axial ligand on charge-transfer and photoreduction processes

Time-resolved resonance Raman spectroscopic measurements were undertaken to probe the axial ligand and solvent effects on the photophysical and photochemical processes of some paramagnetic metalloporphyrins (CuII, CrIII, MnIII and FeIII porphyrins). The presence of odd electrons in d-orbitals of the central metal ions of these metalloporphyrins gives rise to a strong interaction with porphyrin π-electronic system, which affects the energy relaxation pathways of their photoexcited states. The formation and energy of porphyrin ⇋ metal (π,d) or (d,π*) charge-transfer (CT) and metal (d,d) states are sensitive to the solvents employed, especially to the axial ligation ability of the solvents. Based on the change in Raman wavenumbers induced by the structural change in the exciplex formation of photoexcited CuIITPP with the solvents, two intermediate (π,d) CT states below the 2T/4T (π,π*) states are proposed, one being less affected by the ligating solvent (CT1; CuII porphyrins*) and the other strongly influenced by a σ-donor axial ligand [CT2; CuII porphyrins* (ligand)]. As for XCrIIITPP (X = Cl or Br), the photodissociation of axial ligand halogen atoms was observed in benzene. On the other hand, in THF upon photoexcitation, the axial ligand halogen atoms were replaced by the solvent molecules to form the five-coordinate CrIIITPP(THF). A significant reduction in the lifetimes of photoexcited ClCrIIITPP in THF was observed, which is probably due to the participation of the low-lying (π,dπ) CT state in the energy relaxation of the five-coordinate excited CrIIITPP(THF)*. The transient Raman spectra of ClMnIIITPP in THF under intense laser pulse illumination at 416 nm exhibit the spectral features characteristic of MnIITPP. The photoinduced absorption spectra of ClMnIIITPP in THF are also similar to the steady-state absorption spectra of MnIITPP, indicating the photoreduction of MnIII to MnII porphyrins. Upon photoexcitation of ClFeIIIOEP in THF, the photoreduction to yield FeIIOEP(THF) occurred. The photoreduced FeIIOEP(THF) species exist as the high-spin complex, which was confirmed by a comparative analysis of the Raman spectrum of chemically prepared low-spin ClFeIIOEP(pip)2. Copyright © 2000 John Wiley & Sons, Ltd.

Dynamical studies of zeolitic protons and interactions with adsorbates by picosecond infrared spectroscopy

We have investigated zeolite-adsorbate interactions with time-resolved (picosecond) non-linear infrared spectroscopy. In these experiments, the zeolite hydroxyl (the catalytically active, acid site) is vibrationally excited after which the energy relaxation can be monitored real-time. The effect of the presence of adsorbates on energy relaxation rates and pathways provides information on catalyst-adsorbate interaction dynamics. Furthermore, the effect of the presence of adsorbates on the homogeneous linewidth, investigated with infrared hole-burning spectroscopy, provides information on the nature of the interaction potential.

Vibrational energy relaxation of Si–H stretching modes on the H/Si(111)1×1 surface

The vibrational relaxation rate of an excited Si–H stretching mode on the ideally H-terminated H/Si(111)1×1 surface is calculated using Bloch–Redfield theory combined with classical molecular dynamics. The calculated lifetime is found to be in good agreement with the experimental result. Analysis of the power spectrum of the fluctuating force along the Si–H bond suggests that the dominant energy relaxation pathway for the v=1 stretching state is through kinetic coupling to a state with three Si–Si–H bending quanta plus one phonon. The v=2 state is predicted to relax at a considerably higher rate.

Excitation energy relaxation and dimer formation of fluorene in Langmuir—Blodgett monolayer films

Picosecond time-resolved fluorescence has been studied with Langmuir—Blodgett monolayer films containing fluorene as chromophore, in the concentration range of 0.1–29 mol%. Two types of dimer emissions of fluorene were observed. They were assigned as the conformational isomers of fluorene dimers. The dominant energy relaxation pathway is an efficient energy transfer from monomers to dimers.

Vibrational energy transfer on hydrogen-terminated vicinal Si(111) surfaces: Interadsorbate energy flow

We report measurements of excited-state lifetimes for Si–H stretching vibrational modes of steps and terraces on chemically prepared, hydrogen-terminated vicinal Si(111) surfaces using picosecond pump–probe surface spectroscopy. The steps present on these vicinal surfaces are shown to play an important role in the vibrational energy relaxation pathways. Three types of vicinal Si(111) surfaces are studied, all having monohydride-terminated terraces but differing in step termination or in step density. Two surfaces are cut along the 〈1̄1̄2〉 direction, 9° and 5° from the (111) plane, respectively. Both of these surfaces have dihydride-terminated steps. A third surface is cut 9° from the (111) plane along the 〈112̄〉 direction and has monohydride-terminated steps. Two normal modes of the dihydride-terminated steps show vibrational energy relaxation times of ∼100 ps [≤80 ps and 130(20) ps, uncertainty in parentheses], while the monohydride-terminated steps relax 10 times more slowly with an 1100(120) ps lifetime. On the dihydride-stepped 9° surface the lifetime of the terrace mode is shortened to 420(40) ps from the flat surface lifetime of 950(100) ps, while on the monohydride-stepped surface the terrace mode lifetime is 820(80) ps. The results are explained by energy transfer between the terrace and the step Si–H modes. The different dynamics on the monohydride- and dihydride-stepped surfaces arise because the short-lifetime dihydride steps act as energy drains, while the long-lifetime monohydride steps do not. Dipole–dipole coupling between the Si–H stretching modes can account for the interadsorbate vibrational energy transfer observed.

ChemInform Abstract: UV Resonance Raman Examination of the Azurin Tryptophan Environment and Energy Relaxation Pathways

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

UV resonance Raman examination of the azurin tryptophan environment and energy relaxation pathways

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTUV resonance Raman examination of the azurin tryptophan environment and energy relaxation pathwaysJoyce A. Sweeney, Paul A. Harmon, Sanford A. Asher, Cindy M. Hutnik, and Arthur G. SzaboCite this: J. Am. Chem. Soc. 1991, 113, 20, 7531–7537Publication Date (Print):September 1, 1991Publication History Published online1 May 2002Published inissue 1 September 1991https://doi.org/10.1021/ja00020a013RIGHTS & PERMISSIONSArticle Views169Altmetric-Citations27LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (921 KB) Get e-Alerts Get e-Alerts

Ultrafast transient Raman investigation of geminate recombination and vibrational energy relaxation in iodine: The role of energy relaxation pathways to solvent vibrations

Direct observation of geminate recombination and vibrational energy relaxation in the X state of iodine has been accomplished using picosecond Raman spectroscopy. The dynamics of energy relaxation from vibrational levels ranging from v=52 to v=1 have been observed. These levels correspond to absolute energies of 9300 to 210 cm−1 above the zero point in the X potential. The effect of relaxation to solvent vibrations in resonance with I2 vibrations has been studied. The efficiency of these vibrational–vibrational relaxation channels is found to be very solvent dependent. The results suggest that the vibrational coupling between the excited iodine oscillator and the solvent is drastically affected by the nature of the normal mode character of the solvent vibration.

Vibrational energy relaxation processes in heme proteins

Vibrational energy relaxation pathways from optically excited heme proteins are studied using a transient thermal phase grating technique which monitors the solvent lattice temperature. Vibrational energy transfer from the porphyrin ring to the protein backbone leads to extensive delocalization of the energy in the protein helix which is efficiently transferred to the water interface in less than 20 psec. A slower relaxation process on the nanosecond time scale is also observed. The slow relaxation component is attributed to slow conformational relaxation processes of high potential energy states of the heme proteins accessed during the high internal energy conditions of the optically excited molecule.