Vibrational energy transfer and migration processes in matrix isolated CH3F

Abstract

Following excitation ofthe V3 mode in matrix isolated CH 3 F, population of 2V3 is observed. Population of2v3 occurs via intermolecular vibration-vibration (V-V) energy transfer driven by the exothermicity of the anharmonic V -V step equilibrating these states. In the equilibration process, both resonant and nonresonant intermolecular energy transfer processes have been identified. The probabilities of each of these processes have been determined. The phonon assisted nonresonant V-V process has a probability of 3.8 X 10-35 and 6.7 X 10 -35 cm 6 S-I in Xe at 10 and 20 K, respectively. These probabilities were obtained from fluence dependent studies of the rise rate of 2V3 in concentrated matrices. V-V transfer has also been studied in dilute matrices and matrices of intermediate dilution. Signals obtained in these concentration regimes are not exponential but can be reproduced by a Monte Carlo model of V-V transfer. In these matrices there is no longer rapid vibrational energy migration on the time scale of vibrational deactivation. The consequences of the lack of rapid V-V transfer on this time scale are discussed. The difference in energy transfer behavior of CH3F when excited via V3 vs excitation at 3000 cm -I is also rationalized. The temperature dependence and fluence dependence of deactivation rates of V3 excited CH3F are also reported in Ar, Kr, and Xe matrices. By overcoating Ar and Kr matrices with Xe, the temperature range of these measurements has been extended beyond that previously reported.

Wave Packet Study of Ultrafast Relaxation in Ice Ih and Liquid Water. Resonant Intermolecular Vibrational Energy Transfer

“…We label these {q i } i)1 6 in the following sequence: symmetric stretch (water one), asymmetric stretch (water one), bending (water one), and then the three NMs for water number two in a similar sequence. The remaining coordinates, {q i } i) 7 18 , are the standard center of mass coordinates and Euler angles for each molecule. The values of all 18 coordinates are chosen so as to reproduce the dimer equilibrium geometry.…”

“…This fully determines their value, up to an irrelevant value of the whole dimer center of mass coordinates and Euler angles. Afterward, the coordinates {q i } i) 7 18 are frozen at their specific values, to make things simple, not because it is essential for the argument. The dimer intermolecular potential energy can now be Taylor-expanded in the six vibrational NMs around the minimum geometry of the dimer The lowest order term in this expansion, which induces an annihilation of one quantum of, say, symmetric stretch in water one (deactivating state |1〉 ≡ |100000〉) and creates a corresponding quantum in water two (activating state |2〉 ≡ |000100〉), is clearly the quadratic term V′ ≡ R 1,4 q 1 q 4 , since in terms of boson creation and annihilation operators this term equals (ref 30), where ω(sym) and m equal the monomer water symmetric stretch frequency and reduced mass, respectively.…”

“…(iii) The third is resonant energy transfer, where one quantum transfers between two identical molecules, leaving the system with the excitation in the same degree of freedom but transferred to another molecule. Examples are matrix isolated CH 3 F at 10−20 K and the mechanism put forth by Woutersen and Bakker for describing ultrafast OH bond VER in liquid water; see below. For the majority of systems studied so far, mechanisms (i) and (ii) occur faster than the third one, except at low temperatures. , What makes VER even more challenging is the fact that the processes are expected to be quantum mechanical − and, in general, many-body in character, which makes accurate treatments extremely difficult.…”

“…For the majority of systems studied so far, mechanisms (i) and (ii) occur faster than the third one, except at low temperatures. 7,9 What makes VER even more challenging is the fact that the processes are expected to be quantum mechanical [10][11][12][13] and, in general, many-body in character, 14 which makes accurate treatments extremely difficult.…”