HCO production, vibrational relaxation, chemical kinetics, and spectroscopy following laser photolysis of formaldehyde

Abstract

Formaldehyde vapor was photolyzed with a tunable pulsed uv laser. Flash kinetic absorption spectra of the HCO produced were recorded by intracavity dye laser spectroscopy with a time resolution of 1 μs. The energy threshold for radical production was confirmed to be at 86±1 kcal/mole. Photolysis at 294.1 nm produced HCO in its ground vibronic state (∼2/3) and with one quantum of vibrational excitation in either the bending (∼1/3) or CO stretching (10−1–10−2) vibrations. Observation of the CO stretching hot band absorptions allowed that frequency to be determined as 1868.4±1 cm−1. Quantitative, state-resolved measurements of concentration vs time were made in pure H2CO and in mixtures with O2, NO, or Ar. The vibrational relaxation rate for the bending vibration of HCO in collisions with H2CO was (4.3±1) ×10−12 cm3 molecule−1 s−1. Reaction rates for HCO+NO→HNO+CO and HCO+O2→HO2+CO were measured as (1.4±0.2) ×10−11 and (4.0±0.8) ×10−12 cm3 molecule−1 s−1, respectively. Approximate rates were determined for the radical–radical reactions H+HCO→H2+CO and 2HCO→H2CO+CO as 10−9.26±0.3 and 10−10.2±0.5, respectively.