The geometric structure and stability of the NO+·CH4 cationic complex Original Research Article

Ab initio calculationshave been performed, mainly at the MP2 level of theory, using a variety of basis sets, to elucidate the structure of the NO+·CH4 cationic complex. The complex has an equilibrium geometry of Cs symmetry, in which the NO+ moiety eclipses a CH bond of the methane molecule. The geometry is compared to those of related complexes. Harmonic vibrational frequencies are also calculated, together with the interaction energy and some thermodynamic quantities for the complex formation, employing a number of the theoretical methods. In particular, the interaction energy was calculated at the CCSD(T) level of theory. The implications of these results on the resonance-enhanced multiphoton ionization (REMPI) spectroscopy of the NO·CH4 complex are briefly discussed.