Raman spectra and ab initio calculations for methyl nitrite and methyl‐d3 nitrite

Abstract

AbstractThe Raman (4000–10 cm−1) and infrared (4000–80 cm−1) spectra of methyl nitrite, CH3ONO, and methyl nitrite‐d3 were recorded in the gas and solid phases. Additionally, the Raman spectra of the pure liquids were recorded and qualitative depolarization values were obtained. Support for the interpretation of these new data is provided by ab initio calculations using the 6–31G* basis set. Complete equilibrium geometries have been determined for both conformers, as well as structures for every 30° rotation about the NO bond. These calculations give a cis/trans barrier of 4015 cm−1 (11.5 kcal mol−1), a trans/cis barrier of 3504 cm−1 (10.0 kcal mol−1) and an enthalpy difference between conformers of 511 cm−1 (1.5 kcal mol−1) with the cis form being more stable. From a variable temperature Raman study of liquid methyl nitrite‐d3 it is concluded that the cis form is also more stable in this phase with an enthalpy difference between conformers of 262 ± 3 cm−1 (750 ± 9 cal mol−1). A complete assignment of the vibrational fundamentals is proposed based on band contours, depolarization values, group frequencies and shift factors for the two isotopomers. These assignments are supported by normal coordinate analyses using the ab initio force fields to obtain frequencies and potential energy distributions for both conformers.