Translational and vibrational energy distributions in metastable laser pumped polyatomic molecules: A quasithermodynamic description

Abstract

Articles you may be interested inQuantum theory of vibrational, rotational, and translational energy exchange in collisions of polyatomic molecules. Application to methyl halides J. Chem. Phys. 78, 4502 (1983); 10.1063/1.445343Halfcollision description of final state distributions of the photodissociation of polyatomic molecules A model is proposed to describe the metastable vibrational population distribution for a laser pumped polyatomic gas which undergoes vibration-vibration energy exchange on a time scale fast compared to vibration-translation/rotation relaxation. Such systems are shown to be characterized by a multiple temperature distribution with temperature relationships governed by the vibrational energy transfer pathway. In the harmonic oscillator limit each vibrational mode is at a single mode temperature, different from the translational/rotational temperature, leading to simple expressions for the steady state thermodynamic quantities. Additional constraint equations allow the complete determination of the temperature distribution and thermodynamic quantities in terms of two initial parameters, input energy and ambient temperature. Examples of multiple temperature distributions are presented for laser pumped CH3F undergoing various relaxation pathways and at a variety of initial conditions. The selection of the hottest vibrational mode is found to depend only on the path, and this mode may not necessarily be the one with the smallest energy spacing nor the one that is actually pumped. The extent of the vibrational enhancement of this mode is dependent on the initial conditions through the conservation equations. A stable mUltiple temperature condition is found to exist only if a restricted number of energy transfer paths are allowed. E {v I = L: VJE i , g{vJI = IIgvJ ' (9) J , J J where Ej=hll i andg v is the degeneracy of state VJlli' the population of level {t i} can be resolved into its individual mode terms L (F{v I -F{v.l)n{v.l= O. (74) {vi I i J J

~A2.SIGMA.+ .fwdarw. ~X2.PI.i emission spectra of fluoro- and chlorothioboron cations, FBS+ and ClBS+

“…the 2 + -* 2 , transitions of FBS+ and C1BS+. As expected, the spectra are qualitatively similar to those of HBS+ 7 and HCP+. 4 Whereas the emission spectrum of C1BS+ consists of short progressions in the stretching vibrations, in the case of FBS+ strong excitation of the ground-state bending mode is also observed.…”

“…This value is only slightly larger than the one in the 2 , state of HBS+, -322.6 ± 0.4 cm™1. 7 On the other hand, the assignment of the transition to the band at 26 502.7 cm™1 yields A"(X 2 ,) = -370 ± 2 cm.…”

Chirped-pulse millimeter-wave spectroscopy for dynamics and kinetics studies of pyrolysis reactions

“…The vibrational quantum numbers are designated (n 1 , n c 2 , n 3 ), with n 1 representing the CQS stretch (866 cm À1 ), n 2 the bend (520 cm À1 ), n 3 the CQO stretch (2072 cm À1 ), and c the vibrational angular momentum. 36,69 Here we adopt a multi-temperature model 70 in which the vibrational temperature of an individual level n is defined as…”

Vibrational Energy Transfer

“…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.…”