Slow intramolecular vibrational redistribution: the latest results for trifluoropropyne, a comparison with the other terminal acetylenes and the mechanism*

Abstract

We studied the dynamics of intramolecular vibrational redistribution (IVR) from the initially excited mode ν1≈3330 cm−1 (acetylene-type H–C bond) in molecules in the gaseous phase by means of time-resolved anti-Stokes spontaneous Raman scattering. The time constant of this process was estimated as 2.3 ns—this is the slowest IVR time reported so far for the room-temperature gases. We have compared this result with earlier results on the other terminal acetylene molecules, and give an explanation of this low IVR rate. Our suggestion for it follows from an assumption that the most probable doorway state leading to IVR from to the bath of all vibrational–rotational states consists of one quantum of the stretch and two quanta of the bend, and the matter is that the energy defect of Fermi resonance is essentially larger in trifluoropropyne than in other similar molecules. In addition, we have obtained the rate of collision-induced IVR for trifluoropropyne from experiments with various gas pressures and have shown that the observed dynamics is in agreement with a theoretical model assuming strong vibrational–rotational mixing.

Probing the origins of vibrational mode specificity in intramolecular dynamics through picosecond time-resolved photoelectron imaging studies

“…However, although this rule holds in some cases 8 exceptions have been welldocumented for many years, 6,[9][10][11][12][13][14] and factors such as mode-dependence, 15 existence of critical "doorway" states, 4,6,16 molecular flexibility, 17, 18 molecular symmetry 5 and the nature of substituents 8 have all been claimed to play a critical role in determining the course of the dynamics.…”

Intramolecular vibrational redistribution: from high-resolution spectra to real-time dynamics

“…One of the capabilities of time-resolved J-selective spectroscopy is based on a scheme [184,262] in which, along with two stages (excitation and Raman probing), a selective stage is involved: the quasistationary, quasiresonance excitation of an individual J 3 J 1 rotational transition. In this case, coherent directional radiation at the frequency o AS o J1 (where o AS is the anti-Stokes Raman frequency) serves as a signal, which corresponds to one of the four-wave mixing schemes.…”

Molecular spectroscopy and dynamics: a polyad-based perspective

“…One should also mention direct time-dependent measurements of energy flow. 79,93,[110][111][112][113] These most significant areas of contribution to the field of OSD, and probably more, deserve each a specific review and will not be considered further here.…”