High-resolution infrared spectra of the C-H asymmetric stretch vibration of jet-cooled methoxy radical (CH3O)

The high-resolution infrared spectrum of jet-cooled methoxy radical (CH3O) in the region 2850–2940 cm−1 has been recorded at about 26 K in a pulsed slit-jet expansion producing the radical by excimer laser flash photolysis. A perpendicular band centered near 2885 cm−1 was assigned to a portion of the C-H asymmetric stretch vibration (ν4) of CH3O by means of ground-state combination differences. Five ΔP=+1 subbands with P″=−1.5, −0.5, 0.5, 1.5, 2.5, and J″ up to 9.5 have been assigned. Because of the low jet temperature, the assigned transitions all arise from the ground E3/2 fine-structure component of the lowest vibronic state. Preliminary analysis yields values of A, B, and D of 5.232(12), 0.913(8), and 2.5(1.5)×10−5 cm−1, respectively. A small hyperfine splitting was observed in the P″=0.5 series transitions.