High-resolution spectrum of the C–O stretch overtone band in methyl alcohol

Abstract

The Fourier-transform spectrum of the CH3OH overtone C–O stretching band (vCO=2←0) has been recorded in the range 1950–2060 cm−1, at a resolution of 0.004 cm−1. The spectrum is resolved into J multiplets, each displaying complicated substructure due to strong torsion–vibration–rotation effects. Within this structure, it has been possible so far to identify R and P branch transitions for K=0 and K=1 for both A and E torsional symmetry species for J≤24. The assignments are supported by combination differences derived from known ground-state frequencies. The identified branches have been analyzed in terms of effective state-dependent series-expansion parameters, and the leading terms in the torsion–rotation Hamiltonian have been derived for the second excited C–O stretching state. The vCO=2 torsional barrier height is obtained as 395.5±0.2 cm−1, and the effective B value as 23 671.9±1.3 MHz. In addition, the 34.946 cm−1 far-infrared laser line pumped by the 10R(48) CO2 laser line has been tentatively identified as the (nτK,J)v=(031+,16)2→(010+,15)2 transition, and its parent IR pump absorption as the P(031+,17) vCO=2←1 hot-band line.