Observation of an energy threshold for large ΔE collisional relaxation of highly vibrationally excited pyrazine (Evib=31 000–41 000 cm−1) by CO2

Abstract

Energy dependent studies of the collisional relaxation of highly vibrationally excited pyrazine through collisions with CO2 were performed for initial pyrazine energies Evib=31 000–35 000 cm−1. These studies are presented along with earlier results for pyrazine with Evib=36 000–41 000 cm−1. High-resolution transient IR laser absorption of individual CO2 (0000) rotational states (J=56–80) was used to investigate the magnitude and partitioning of energy gain into CO2 rotation and translation, which comprises the high energy tail of the energy transfer distribution function. Highly vibrationally excited pyrazine was prepared by absorption of pulsed UV light at seven wavelengths in the range λ=281–324 nm, followed by radiationless decay to pyrazine’s ground electronic state. Nascent CO2 (0000) rotational populations were measured for each UV excitation wavelength and distributions of nascent recoil velocities for individual rotational states of CO2 (0000) were obtained from Doppler-broadened transient linewidth measurements. Measurements of energy transfer rate constants at each UV wavelength yield energy-dependent probabilities for collisions involving large ΔE values. These results reveal that the magnitude of large ΔE collisional energy gain in CO2 (0000) is fairly insensitive to the amount of vibrational energy in pyrazine for Evib=31 000–35 000 cm−1. A comparison with earlier studies on pyrazine with Evib=36 000–41 000 cm−1 indicates that the V→RT energy transfer increases both in magnitude and probability for Evib>36 000 cm−1. Implications of incomplete intramolecular vibrational relaxation, electronic state coupling, and isomerization barriers are discussed in light of these results.

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

“…Similar onsets have been observed in energydependent studies of the pyrazine/CO 2 system. [17][18][19] Mullin and co-workers observed similar changes to T rot , T trans , and k 2 J between 286 and 281 nm. In those studies, T rot , T trans , and k 2 J increased by 26%, 32%, and a factor of 2, respectively.…”

A unified model for simulating liquid and gas phase, intermolecular energy transfer: N2 + C6F6 collisions

“…34,35,37 Mullin et al have applied [39][40][41][42][43][44][45][46][47][48][49] high resolution infrared laser transient absorption spectroscopy to study energy transfer from pyrazine, 39,[42][43][44][45][46]49 pyridine, 41,48 hexafluorobenzene, 40 and azulene. 47 Flynn studied relaxation of benzene, 50 benzene-d6, 50 hexafluorobenzene, 50,51 and pyrazine 51 in collisions with CO 2 using time resolved diode laser spectroscopy.…”

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.…”

“…28,57 Studies on the energy dependence of P(EЈ,E) in these single collision experiments require a corresponding variation of the excitation energy, currently in the range between 31 000 and 41 000 cm Ϫ1 . 58,60 With their specific data on the role of the V, R, T relaxation channels such state resolved measurements on the energy accepting particle provide ideal, complementary information on CET obviously not directly available from KCSI studies on the energy loss of the relaxing donor molecules at high densities of states.…”