Time-resolved observation of intermolecular vibrational energy transfer in liquid bromoform

Abstract

Efficient intermolecular energy transfer between the C–Br stretching modes ν2 and ν5 of bromoform molecules in the liquid phase has been observed directly in time-resolved experiments applying vibrational pump–probe spectroscopy with picosecond laser pulses. An analysis of results on CHBr3, CDBr3, and an isotopic mixture of both yields a typical time constant of 25±15 ps for this rather efficient, near-resonant intermolecular relaxation channel. Additional new details about the intramolecular pathways of vibrational energy relaxation have been determined for the pure substances.

Evidence for Cooperative Vibrational Relaxation of the NH-, OH-, and OD-Stretching Modes in Hydrogen-Bonded Liquids Using Infrared Pump-Probe Spectroscopy

“…Hence the fact that comparable efficiencies are observed for the two relaxation channels suggests that the anharmonic interactions that couple the excited and accepting modes should be of comparable magnitude for the two relaxation channels; that is, the intermolecular anharmonic potential-energy terms of type Q A;stretch Q A;accept Q B;accept (with Q normal-mode coordinates and A, B indicating different molecules) should be comparable to the intramolecular anharmonic terms of type Q A;stretch Q 2 A;accept . Such high intermolecular anharmonicities might arise from the strong intermolecular interactions in hydrogen-bonded liquids, as seems to be confirmed by the observation that in neat liquid CHBr 3 and CDBr 3 , the CH-and CD-stretch relaxation rates are the same as in a 1:1 isotopic mixture [14]. It cannot be determined from our data which specific intramolecular accepting modes are involved in the proposed bimolecular relaxation mechanism.…”

Vibrational relaxation of CH3I in the gas phase and in solution

“…8,24 Pump-probe experiments directly observe energy flow within and out of a molecule by exciting a nonstationary vibrational state with one laser pulse and then probing the evolution of the system as a function of time with a second pulse. 25,26 Infrared absorption, [27][28][29][30][31][32] anti-Stokes Raman scattering, [33][34][35][36][37] and ultraviolet absorption [38][39][40][41][42][43][44][45][46][47][48][49] are the most common methods for probing the vibrational dynamics in the ground electronic state and are generally most useful in the condensed phase where it is possible to obtain a high density of vibrationally excited molecules. In fact, there are relatively few timeresolved studies of IVR in the ground electronic state for gas phase systems.…”

Chemical dynamics of vibrationally excited molecules: Controlling reactions in gases and on surfaces

“…Studying the fate of an initially energized molecule requires time resolution on the order of the characteristic few hundred femtosecond encounter time, and modern ultrafast laser technology puts experiments in that regime. The most extensive studies of vibrational dynamics in liquids follow the historical pattern of first assessing energy transfer (25), and there are recent examples (54)(55)(56)(57)(58)(59)(60)(61)(62)(63)(64)(65)(66)(67)(68)(69) that particularly address the relaxation of COH stretching excitations. The general picture that emerges from these studies is that in relatively weakly interacting solvents, such as chloroform, the vibrational state structure and couplings of the molecule influence the energy flow within the initially excited molecule most strongly.…”