State-Resolved Studies of Collisional Quenching of Highly Vibrationally Excited Pyrazine by Water:  The Case of the Missing V → RT Supercollision Channel

Abstract

The quenching of highly vibrationally excited pyrazine through collisions with H2O at 300 K in a low-pressure environment was investigated using high-resolution transient absorption spectroscopy of water at λ ≈ 2.7 μm. Highly vibrationally excited pyrazine with E vib = 37 900 cm-1 was prepared by absorption of 266 nm light to the electronically excited S2 state, followed by rapid radiationless decay to the ground electronic state. Collisions between highly excited pyrazine and water that result in rotational and translational excitation of the vibrationless ground state of H2O (000) were investigated by measuring the state-resolved appearance of individual rotational states of H2O (000). Transient absorption measurements have been made on numerous rotational states to determine the nascent distribution of rotational energy gain in water. Doppler-broadened transient absorption line shapes were collected for a number of rotational levels in the (000) state in order to measure velocity distributions of the scattered water molecules. The nascent distribution of water rotational states with E rot > 1000 cm-1 is well described by T rot = 920 K, and the velocity distributions correspond to T trans ≈ 560 K, independent of the rotational state. Rate constants for energy gain into individual quantum states of H2O (000) from collisions with hot pyrazine provide a measure of the high-energy part of the energy-transfer probability distribution function. The quenching of hot pyrazine through collisions with water displays a significant reduction in the bath translational energy gain when compared to earlier studies on the quenching of hot pyrazine (E vib = 37 900 cm-1) by CO2 {Wall, M. C.; Mullin, A. S. J. Chem. Phys. 1998, 108, 9658}. A comparison of the two systems provides insights into the molecular properties that influence the relaxation of highly vibrationally excited molecules.

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). 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.…”

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.…”