Multiphoton ionization spectroscopy and vibrational analysis of a 3p Rydberg state of the hydroxymethyl radical

The resonance enhanced multiphoton ionization (REMPI) spectra of CH₂OH, CH₂OD, CD₂OH, and CD₂OD between 420-495 nm are reported. Analysis of the excited state vibrational band progressions shows that the spectrum originates from simultaneous two photon absorption to form a 3p Rydberg state (ν₀₀=40 064 cm^-1) of the radical. Absorption of a third photon ionized the radical. A normal mode analysis of the REMPI spectra enabled assignments of six active vibrational modes in the excited state. The no isomerization of methoxy radicals into hydroxymethyl radicals was observed. The experimental measurement uncertainty limits this isomerization rate to less than 2.9 s^-1 at 300 K.