The Ã2Σ+←2Π transition of the NO·CH4 and NO·CD4 complexes

Abstract

NO·CH₄ and NO·CD₄ were studied in a molecular beam, using (1 + 1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy. A detailed spectrum results in each case, with a series of bands observed, assigned to intermolecular vibrations onto which is superimposed further structure. The origin of this further structure is discussed in the light of previous studies. From the spectrum, a number of intermolecular vibrational frequencies in the à state were obtained. D₀^′ for NO·CH₄ (NO·CD₄) was measured as 211 (238) cm⁻¹; with D₀^″ for NO·CH₄ (NO·CD₄) being derived as 117 (122) cm⁻¹. Ab initio calculations were performed on the state, and it is deduced that the state has a C_s global minimum, with the NO pointing towards a CH₃ face, with the N tilted towards the methane. That said, from the energetic proximity of a number of stationary points, the complex is expected to be performing wide amplitude motion, sampling a wide range of energies even with the zero-point energy.