Rotationally Resolved Infrared Spectroscopy of the Hydroxymethyl Radical (CH₂OH)

Abstract

Infrared spectra of CH2OH have been recorded in the molecular beam using a combination of depletion and double resonant ionization detected IR (DRID-IR) spectroscopy via the 3pz Rydberg state. With DRID-IR spectroscopy, IR transitions are detected by exciting CH2OH in a selected vibrational level in the ground state to a Franck−Condon favorable level in 3pz from which it is ionized. Rotationally resolved spectra of the fundamental CH symmetric stretch (ν3), CH asymmetric stretch (ν2), OH stretch (ν1), and the first OH-stretch overtone (2ν1) are obtained. The rovibrational structure is analyzed with the aid of ab initio calculations and asymmetric rotor simulations. The OH and CH symmetric stretch fundamentals are hybrid a/b-type bands. On the other hand, a pure b-type transition is observed for the CH asymmetric stretch fundamental. The spectrum of the first overtone of the OH stretch is rotationally resolved, indicating that intramolecular vibrational redistribution (IVR) is not extensive. The rotational linewidth, however, is ∼0.8 cm-1, greater than the laser-limited linewidth observed for the fundamental transitions (∼0.4 cm-1). Reasons for the increase in linewidth are discussed.