Diode laser study of the ν2 band of the methyl radical

Abstract

The v2 = 1←0, 2←1, and 3←2 bands of the methyl radical were observed in the gas phase by infrared tunable diode laser spectroscopy at 606.4531, 681.6369, and 731.0757 cm−1. The observed vibration–rotation spectra were analyzed to derive precise values for the rotational constants, centrifugal distortion constants, and spin–rotation interaction constants. The absence of N = odd, K = 0 levels in the v2 = even states and of N = even, K = 0 levels in the v2 = odd states was confirmed, indicating that each vibrational state is nondegenerate. The observed band origins, when analyzed, led to a potential function for the out-of-plane bending vibration that has no potential hump at the planar configuration. The large negative anharmonicity of this potential was ascribed to a vibronic interaction with excited electronic states. The methyl radical was generated by a 60 Hz discharge in di-tert-butyl peroxide and was found to have a lifetime of about 1.4 msec; its concentration in the absorption cell was estimated to be about 1013 molecules/cm3, provided that a recombination reaction is the only route for eliminating methyl radicals.

Photodissociation spectroscopy and dynamics of CH3O and CD3O

“…57 The distribution functions f n (E T ) are 58 with an asymmetric tail extending to lower translational energy, i.e., toward higher rotational energy. The shape of this function is identical for every vibrational peak in a given spectrum.…”

On the Reaction Kinetics of Chemically Active Molecular Microwave Plasmas

“…al produced CH 3 by flash photolysis of CH 3 I [28]. Much higher sensitivity and resolution was later achieved by Hirota and co-workers using Tuneable Diode Laser Absorption Spectroscopy (TDLAS) [29][30][31]. Later, Celii and co-workers detected the absorption spectrum of the methyl radical in a hot filament CVD reactor using TDLAS [77].…”

“…In 1981, in their seminal work on the infrared laser spectroscopy of the ν 2 band of CH 3 using TDLAS Yamada, Hirota and Kawaguchi [82] assumed a value of 0.1 Debye for the transition dipole moment of the ν 2 fundamental based on the absolute intensity of their data and by analogy with the ν 2 band of ammonia (0.3 Debye). Shortly afterwards Yamada and Hirota [78] made the first direct measurement of µ 2 .…”

From High-Resolution Spectroscopy to Chemical Reactions

“…When we completed our time-resolved spectroscopic system, we chose the CH,I photolysis to test our method (57), because we have extensive data on the V2 mode (31). Because an inverted distribution was reported in the literature, we expected to observe induced emission for the V 2 band, as in our study on SO generated by the 193-nm photolysis of S02 (48).…”