Theoretical Studies On Ro-vibrational Spectra Of He-N₂O And Ar-HCCCN

The weak intermolecular forces for van der Waals (vdW) complexes between rare gas (Rg) atoms and linear molecules have attracted considerable interest recently. The spectroscopy of these complexes can provide very useful information on their geometries and intermolecular dynamics. In this work, we have studied the He-N2O and Ar(HCCCN complexes using supermolecular method at coupled-cluster single double (triple) [CCSD(T)] and the fourth-order Moller-Plesset (MP4) levels respectively. 1 A new ab initio intermolecular potential energy surface has been calculated for the He-N2O complex with N2O at its ground vibrational state using a supermolecular approach. The calculations were performed at the CCSD(T) level with a large basis set including midpoint bond functions. The CCSD(T) potential is found to have two minima corresponding to the T-shaped and the linear He-ONN structures. The T-shaped minimum is the global minimum. The two-dimensional discrete variable representation (DVR) method was employed to calculate the rovibrational energy levels for 4He-N2O and 3He-N2O with N2O at its ground and excited states. In addition, the frequencies and line intensities of the rotational transitions in theregion of N2O have been calculated for the ground and the first excited intermolecular vibrational states. The calculated transition frequencies and the intensities are in good agreement with the observed results.2 An ab initio intermolecular potential energy surface of the Ar(HCCCN complex has been obtained using a supermolecular method. The calculations were performed at the MP4 level. The complex was found to have a planar T-shaped structure minimum and a linear minimum with the Ar atom facing the H atom. The T-shaped minimum is the global minimum. The two-dimensional DVR was employed to calculate the rovibrational energy levels for Ar(HCCCN. The rovibrational spectra including intensities for the ground state and the first excited intermolecular vibrational state are also presented. The calculated spectra can reproduce the available observed spectra very well.