The torsion-vibration spectrum of methanol trapped in neon matrix

The spectra of six isotopic species of methanol trapped in neon matrix have been recorded between 30 and 11,000 cm−1. Noticeable temperature effects are observed for the OH species. They allow two kinds of absorptions to be identified for most of the vibrational transitions: those low temperature (LT) predominating at 2.7 K and those high temperature (HT) significantly increasing in intensity when varying temperature from 2.7 to 7 K. The conversion is perfectly reversible and has been examined from two points of view: the kinetics of interconversion and the activation energy associated to the process. The kinetic study shows that the limiting factor of the measurements is the time required for spectral acquisition (about 5 s). The activation energy deduced from Arrhenius plots is found equal to 6.7 ± 0.5 cm−1. From the comparison with gas phase data one concludes that the internal rotation about the C-O bond is not strongly altered by the matrix surrounding, the activation energy corresponding to the E-A tunneling splitting of the ground state (9.12 cm−1 for CH3OH in the gas phase). The pure torsion and the torsion-vibration spectra are generally consistent with those in the gas phase. In particular the complex structure of the COH bending mode is well reproduced, with a clear identification of the transitions issuing from the A and E sublevels of the ground state.