S. H. Lin

Effect of Partial Deuteration and Temperature on Triplet‐State Lifetimes

The lifetime of the triplet state of aromatic molecules increases when deuterons are substituted for its protons. For naphthalene, our experiments and others show that the decay rate is linear with the number of protons and independent of the position of substitution. This result is shown to follow from Lins theory of nonradiative decay of excited states.

On the master equation approach of vibrational relaxation in condensed media

The purpose of this paper has been to examine the validity and limitations of the Pauli master equation and to demonstrate the use of the master equation approach in describing the vibrational relaxation in the condensed phase. The master equations for vibrational relaxation of a number of model systems have been derived. The calculation of rate constants of vibrational relaxation has been discussed. The solution of the master equations of multimode relaxation at low temperatures has been presented. The Brownian motion of an oscillator linearly coupled with the medium has been investigated and a model of the coupling between the vibrational relaxation and other unimolecular processes (like electronic relaxation, etc.) has been developed.

Theory of vibrational relaxation and infrared absorption in condensed media

In this paper, we develop a theoretical model for vibrational relaxation of vibrons in condensed media based on the breakdown of the adiabatic separation of vibron (high frequency) and phonon (low frequency) motion. The conditions under which the adiabatic approximation of the vibron–phonon system is valid are examined. The present model is also applied to the ir absorption in condensed media; the band shape function and the dipole correlation function are obtained. The relation between the vibrational relaxation and the ir absorption is discussed.

Radiationless transitions in isolated molecules

The radiationless decay rate constant of a single vibronic state and the equilibrium average nonradiative decay rate constant of an isolated molecule have been shown to be obtainable from the appropriate inverse Laplace transforms of the thermal average rate constants. An expression of the nonradiative decay rate constant of a single vibronic state, including the frequency changes, has been derived and has been compared with that obtained by Nitzan and Jortner and with that obtained by Heller et al. The microcanonical average rate constant has been shown to be to be derivable from the thermal rate constant by replacing β[β = (kT)−1] in the thermal rate constant by the corresponding β* of the isolated system, which is to be determined from the energy of the system.

Effect of temperature and quencher concentration on vibrational relaxation in condensed media

In this paper, we are concerned with the temperature effect on vibrational relaxation and the vibrational energy transfer from the vibrationally excited donor to the acceptor. For the temperature effect, we present numerical results to show the temperature dependence of the rate constant of vibrational relaxation and to discuss the validity of the rate constants obtained from the use of the weak coupling approximation and the strong coupling approximation. It is shown that although the temperature effect is extremely large over the temperature range T=0 to T=ϑE, the Einstein temperature of the medium, for the temperature range T=0 to T=0.3 ϑE, the rate constant varies slowly with temperature. For the vibrational energy transfer, we derive the master equation to describe the time dependent behavior of the excited donor, and the expression for the rate constant of vibrational energy transfer. The master equation is solved to study the temporal behavior of the excited donor as a function of the acceptor conc...

Theory of photoinduced intramolecular electron transfer in condensed media

In this paper, we are concerned with the theoretical treatment of intramolecular electron transfer (ET). In particular we are interested in the effect of the chemical groups connecting between donor and acceptor groups on electron transfer. We treat two cases. Type 1 refers to the situation where the energy difference between the LUMO of the connecting groups and the LUMO of the donor group is much larger than vibrational energies. Type 2 refers to the situation where the energy difference between the LUMO of the connecting groups and the LUMO of the donor group is comparable to vibrational energies. We show that Type 1 ET is similar to the Raman scattering while Type 2 ET is similar to the resonance Raman scattering.

Experimental and theoretical studies of resonance Raman scattering: Temperature effects in β‐carotene

The Raman excitation profile of β‐carotene in isopentane solution has been measured at 118 and 298 K using stilbene dye laser excitation as well as argon laser lines. This data as well as absorption data have been analyzed by using a model which includes the conventional multimode and band shape function. With this model, the parameters of normal coordinate displacement and damping constant, and the effect of temperature and band shape function on the width and peak position can be explored. Using the same set of parameters, we have successfully fit the absorption spectra and the resonance Raman excitation profile of three fundamental bands at both low temperature and room temperature. With our approach the damping factor is found to be on the order of 50 cm−1 for β‐carotene.

Two-dimensional spectroscopy: Theory of nonstationary, time-dependent absorption and its application to femtosecond processes

In this paper, we present a formalism for a generalized linear susceptibility applicable to femtosecond (fs) processes. As an application, we analyze the recent experimental results of the real‐time fs transition spectra of the photodissociation of NaI and NaBr reported by Zewail et al. In this connection we also investigate in general the behaviors of decaying and trapping of the molecule in an excited electronic state coupled to a continuum.

Shifts in fluorescence excitation spectra of anthracene-argon van der waals complexes

Abstract In this paper we present experimental results on van der Waals complexes of anthracene with argon formed in a hypersonic jet expansion. We have recorded the flourescence excitation spectra for anthracene seeded in an argon carrier gas for various pressures of argon and have detected complexes with up to ten bound argon atoms. We then analyse these results by applying the theory of solvent effect on electronic spectra developed by Longuet-Higgins and Pople [1] and derive equations which predict the spectral upon complexation. The data lend credence to a model which considers an inner solvation shell of four Ar atoms. with successive atoms being in a next nearest environment.

A theoretical study of resonance Raman scattering from molecules

The main purpose of this paper has been to study the high pressure effect on the resonance Raman scattering (RRS) of molecules in a dense medium. In deriving the RRS cross section under high pressure, a different approach from that presented in the previous papers has been used, and the resulting expression for the RRS cross section can be used to treat both pressure and temperature effects.