Translational and rotational excitation of the CO2(000) vibrationless state in the collisional quenching of highly vibrationally excited perfluorobenzene: Evidence for impulsive collisions accompanied by large energy transfers

Abstract

Translational and rotational excitation of the CO 2 (00 0 0) vibrationless state in the collisional quenching of highly vibrationally excited perfluorobenzene: Evidence for impulsive collisions accompanied by large energy transfers Classical trajectory calculations of the rate of collisional energy transfer between a bath gas and a highly excited polyatomic method, and the average energy transferred per collision, as functions of the bath gas translational energy and temperature, are reported. The method used is that of Lim and Gilbert [J. Phys. Chem. 94, 72 (1990)], which requires only about 500 trajectories for convergence, and generates extensive data on the collisional energy transfer between Xe and azulene, as a function of temperature, initial relative translational energy (E T)' and azulene initial internal energy (E'). The observed behavior can be explained qualitatively in terms of the Xe interacting in a chattering collision with a few substrate atoms, with the collision duration being much too brief to permit ergodicity but with a general tendency to transfer energy from hotter to colder modes (both internal and translational). At thermal energies, trajectory and experimental data show that the root-mean-squared energy transfer per collision, (ali 2) 112, is relatively less dependent on E' than the mean energy transfer (ali). The calculated temperature dependence is weak: (AE 2) 112 0:: To. 3 , corresponding to (AE down) 0:: To. 23 • Values for the calculated average rotational energy transferred per collision (data currently only available from trajectories, and required for falloff calculations for radical-radical and ion-molecule reactions) are of the order of k B T, and similar to those for the internal energy; there is extensive collision-induced internal-rotational energy transfer. The biased random walk "model B," as discussed in text, is found to be in accord with much of the trajectory data and with experiment. This suggests that energy transfer is through pseudorandom mUltiple interactions between the bath gas and a few reactant atoms; the "kick" given by the force at the turning point of each atom-atom encounter governs the amount of energy transferred. Moreover, a highly simplified version of this model explains why average energies transferred per collision for simple bath gases have the order-of-magnitude values seen experimentally, an explanation which has not been provided hitherto.

Collisional energy transfer probabilities of highly excited molecules from kinetically controlled selective ionization (KCSI). II. The collisional relaxation of toluene: P(E′,E) and moments of energy transfer for energies up to 50 000 cm−1

“…[20][21][22][23][24] Others have monitored the uptake of energy in the bath medium during the relaxation by various techniques [25][26][27][28][29][30][31][32][33][34] or even identified state-specifically the energy transferred, e.g., to CO 2 colliders in single collisions. [35][36][37][38][39][40][41][42] The vast majority of those data are on ͗⌬E͘, the average amount of energy transferred per collision. Among the reported energy dependent ͗⌬E͘, many rather surprising differences and unusual variations are reported, even for the same relaxing species in standard bath gases, and the reasons for such cases are usually not clear.…”

“…Very valuable and detailed experimental data on inelastic collisions have recently been obtained from diode laser spectroscopy of the bath gas, which allows full rotational, vibrational and translational information on the result of a single collision. [35][36][37][38][39][40][41]47 Fully state-resolved observation of the energy transfer on the acceptor side, which characterized part of the far downward wing of P(EЈ,E) ͑i.e., at a restricted range of large ⌬E values͒, have so far been possible for CO 2 as a collider. To put the measured ''partial'' P(EЈ,E) data from these measurements on an absolute scale involves a non trivial problem of suitable normalization.…”

Rotationally Resolved IR-Diode Laser Studies of Ground-State CO2 Excited by Collisions with Vibrationally Excited Pyridine

“…As also seen in previously studied systems, 3,9,10,21 singleexponential fitting of P(E,E′) provides a poor fit to the experimentally obtained distribution function, when normalization and detailed balance are considered; however, the biexponential model accurately fits the data with those restrictions. The normalized, biexponential model, which has been used to include both strong and weak collisions, is given for down collisions according to 35 …”

Determination of the collisional energy transfer distribution responsible for the collision-induced dissociation of NO2 with Ar

“…Supercollisions were first detected experimentally by Flynn and co-workers through high-resolution, diode laser transient absorption spectroscopy on collisionally excited (rotationally and translationally) CO 2 as a collision partner of a very vibrationally hot perfluorobenzene molecule [19]. These experiments are sensitive to the strong collisions that transfer large amounts of energy to the rotational and translational degrees of freedom of the CO 2 collision partner.…”