High-Resolution Direct-Absorption Spectroscopy of Hydroxymethyl Radical in the CH Symmetric Stretching Region

Abstract

High-resolution, fully rotationally resolved direct absorption spectra of hydroxymethyl radical, CH2OH, are presented in the infrared CH stretching region. As a result of low rotational temperatures and sub-Doppler linewidths obtained in the slit supersonic expansion, the Ka = 0 ← 0 band of the symmetric CH stretch for CH2OH has been unambiguously identified and analyzed. By way of chemical confirmation, hydroxymethyl radical is generated via two different slit jet discharge syntheses: (i) direct dissociation of CH3OH to form CH2OH and (ii) dissociation of Cl2 followed by the radical H atom extraction reaction Cl + CH3OH → HCl + CH2OH. The identified transitions are fit to a Watson A-reduced symmetric top Hamiltonian to yield first precision experimental values for the ground state rotational constants as well as improved values for the symmetric stretch rotational constants and vibrational band origin. The results both complement and substantially improve upon spectral efforts via previous double resonance ionization detected infrared methods by Feng et al. [J. Phys. Chem. A, 2004, 108, 7093], as well as offer high-resolution predictions for laboratory and astronomical detection of hydroxymethyl radical in the millimeter-wave region.