Infrared spectrum of the CH3OH-CO complex in the C-O stretching region

The infrared spectrum of the weakly-bound molecular complex methanol - carb on monoxide has been observed, for the first time in the gas phase, by mean s of a parallel (DeltaK = 0) band in the region of the carbon monoxide C-O stretching vibration. The band origin, 2154.5 cm(-1), represents a blue shi ft of 11.2 cm(-1) relative to the free CO molecule; its proximity to that o f the H2O - CO complex points to a similarity of the hydrogen bonding in th e two systems. The observed structure of the band could be well reproduced by a simulation based on the methyl internal rotation component of A-symmet ry. A component of E-symmetry must also be present, with roughly equal inte nsity, but the two components were not individually resolved. The observed transitions showed evidence of predissociation broadening, leading to an es timate of t greater than or similar to 0.5 ns for the lifetime of the upper (C-O stretching) state.