Laser induced combination band fluorescence study of vibrational deactivation of ethylene in C2H4-X mixtures

Abstract

Laser induced fluorescence studies of vibrational deactivation of C2H4 in mixtures with rare gases and diatomic molecules have been made. The experimental results are compared with predictions based on simple vibration-translation and vibration-rotation energy transfer theories. The data is consistent with V-T deactivation of ethylene by light collision partners. For heavy collision partners the experimental results cannot be reasonably described using standard V-T theory. The qualitative trends in the deactivation probability for the heavy collision partners are in the direction predicted by simple, semiempirical V-R calculations.

Vibrational Energy Transfer

“…Here we refer to collisions which change the energy of the initially prepared state, and not intramolecular vibrational relaxation (IVR) in which vibrational energy is redistributed among the different modes without a change in total energy. The rates and mechanisms for V−V energy transfer processes were subsequently determined for many small molecules, − and the role of both long- and short-range intermolecular forces in mediating such energy exchange events was delineated. − Progress included both an understanding of the fundamental processes which controlled the exchange of energy between chemically distinct molecules and the rates and mechanisms by which different vibrational modes in the same molecule were equilibrated by collisions. In addition, excellent coupling between theory and experiment was made for the first time through the study of the temperature-dependent vibration to translation/rotation energy transfer probability in H 2 , a molecular system sufficiently small to be theoretically tractable. − For small molecules a general result of these laser-based energy transfer studies was the “unfortunate” realization that collision-induced mode-to-mode vibrational relaxation almost always proceeds faster than bimolecular chemical reaction. ,− Thus, in any environment where multiple collisions occur on the time scale of a chemical reaction, the vibrational modes of a polyatomic molecule will equilibrate, and reaction occurs without the advantage of energy localization in a single mode.…”

Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) Detection of the ν7 Band of Ethylene at Low Pressure with CO2 Interference Analysis

“…The fitting results are summarized in Table 1, which are in relatively good agreement with the previously measured values in the literature. 31 As illustrated in Figure 8…”

“…VT relaxation time of C 2 H 4 at the n 10 state obtained in this work. VT relaxation time of C 2 H 4 at the n 10 state measured by Yuan and Flynn 31.…”

Energy Relaxation Dynamics of Photofragments Measured by Probe Beam Deflection Technique: Photodissociation of CF3I at 266 nm

“…By analyzing the time-resolved PBD signals, we determined the excess energy partitioning between various modes of photofragments as well as their relaxation rates. The results were compared with the energy partitioning of CF 3 I photofragments measured by the PTS method 22 and V−T and E−T transfer rates of chemical species reported previously. ,, Apart from its simplicity, the PBD method provided results similar to the ones measured by highly sophisticated methods such as PTS, inferring its applicability to the study of the dynamics of energy transfer during and after the photodissociation.…”

“…We found that the observed V−T transfer rate constant of CF 3 to Ar obtained in the PBD study, 8.0 × 10 2 s -1 Torr -1 , is similar to the ones of several molecules excited to low vibrational levels. For example, the V−T rate constant of C 2 H 4 to Ar when C 2 H 4 was pumped to the ν 7 (949.2 cm -1 ) vibrational mode was reported as 4.7 × 10 2 s -1 Torr -1 , and that of CCl 2 F 2 excited to the ν 6 (922 cm -1 ) mode was 8.6 × 10 3 s -1 Torr -1 . Also, the V−T transfer rate constant of a stable radical NO 2 to argon, in which NO 2 is in the (010) state, was reported as 1.8 × 10 3 s -1 Torr -1 .…”