“Supercollision” energy dependence: State-resolved energy transfer in collisions between highly vibrationally excited pyrazine (Evib=37 900 cm−1 and 40 900 cm−1) and CO2

Abstract

The quenching of highly vibrationally excited pyrazine through collisions with CO2 is investigated as a function of initial pyrazine internal energy using a high-resolution laser transient absorption spectrometer. Experiments focus on energy exchanging collisions that result in excitation of rotations and translations in the ground vibrationless (0000) state of CO2. Highly vibrationally excited pyrazine (Evib=37 900 cm−1 or Evib=41 000 cm−1) is prepared via pulsed excitation at 266 nm or 246 nm, followed by rapid radiationless decay to the ground electronic state. The nascent CO2 rotational populations are measured by collecting the transient absorption of individual rovibrational lines at short times following the pyrazine excitation. The translational energies of CO2 recoiling from hot pyrazine are measured for numerous individual rotational levels. Energy dependent rate constants and probabilities are reported for both donor energies and results are compared with earlier studies using 248 nm excitation. These experiments reveal that for both donor energies, significant rotational and translational excitation of CO2 results from collisions with highly vibrationally excited pyrazine, as evidenced by the similarity in the observed rotational and translational distributions. Remarkably, however, the probabilities for the individual energy transfer pathways increase by as much as a factor of 3 for a 7% change in the pyrazine internal energy. The magnitudes and probabilities of energy transfer are described in terms of an energy transfer distribution function for the different donor molecule energies and implications for sequential quenching collisions are discussed.

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

“…48,49 In addition, KCSI experiments on energy transfer in highly excited pyrazine and pyridine have already been completed in our laboratory. 86 They will allow us to compare the KCSI results with independent measurements of high ͉EЈϪE͉ sections of P(EЈ,E) curves from quantum state resolved scattering data, 36,40 and with results from IRF studies. 20,21…”

“…From the point of dynamics of inelastic scattering, an experiment studying a single collision event, like in CO 2 diode laser spectroscopy, [35][36][37][38][39][40] is of course closer to the heart of physics. However, in these investigations only the initial collisions with low rotational temperature are observed which differ from the typical ones in relaxations under thermal conditions.…”

“…[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.…”

Collisional energy transfer probabilities of highly excited molecules from kinetically controlled selective ionization (KCSI). I. The KCSI technique: Experimental approach for the determination of P(E′,E) in the quasicontinuous energy range

“…[52][53][54] A different type of experiments extracts information by observation of the acceptor molecule in the CET process. 27,28,[42][43][44][45][46][47][48][49][50][51][55][56][57][58][59][60] Flynn, Mullin, and co-workers, e.g., have used a quantum state resolved scattering technique, applying high resolution diode or F-center laser spectroscopy to study CET of highly vibrationally excited molecules, as, e.g., pyrazine, by monitoring the energy uptake of the collider. 27,28,55 Experiments have been applied to a variety of systems involving CO 2 , CO, N 2 O, and H 2 O as acceptor molecules, 61,62 and extension to other colliders and excitation energies would be valuable.…”