Jet-cooled infrared spectrum of methoxy in the CH stretching region

Abstract

Observations of the jet-cooled infrared spectrum of CH₃O in the CH stretching region have been extended, down to 2756 cm⁻¹ and up to 3003 cm⁻¹. In the lower frequency extension, a single vibronic band has been assigned. In the higher frequency region, the spectrum becomes complex above 2900 cm⁻¹ and remains so until near 2970 cm⁻¹ where it rapidly becomes sparse. Including the single vibronic band previously reported, a total of four bands have been assigned. Two bands including the original one follow a perpendicular ΔP = +1 rotational selection rule and the other two bands follow a parallel ΔP = 0 selection rule. In addition to these in the congested region between 2900 and 2970 cm⁻¹, ten isolated sub-bands (two P″ = −1/2, two P″ = +1/2, and six P″ = +1.5) have been assigned, but it has so far not been possible to connect these together to form bands. Taken together these observations suggest that there are strong vibronic couplings between the two CH stretching vibrations and the overtone and combination levels in the region.