Rovibrational states of Ar–HCN van der Waals complex: A localized representation calculation

All bound rovibrational states of Ar–HCN and Ar–DCN van der Waals complexes for J=0–10 are calculated, assuming frozen HCN (DCN). The calculations are performed using the recently developed approach for accurate and efficient computation of highly excited rovibrational states of floppy triatomic molecules [M. Mladenović and Z. Bac̆ić, J. Chem. Phys. 93, 3039 (1990)]. Matrix representation of the Hamiltonian in body-fixed Jacobi coordinates is formed by combining the discrete variable representation of the angular coordinate and distributed Gaussian basis for the radial degree of freedom. The coupled low-frequency large amplitude vibrations are treated accurately, without any dynamical approximation. Model 2-D (R,θ) potential surface by Dykstra, having two minima at collinear Ar–HCN and Ar–NCH geometries, is employed. Besides energy levels and wave functions, for each state we calculate expectation values of Jacobi coordinates, 〈R〉 and 〈θ〉, degree of wave function delocalization, and effective rotational constants (for some states). Majority of states of Ar–H/DCN are delocalized over both potential minima. Comparison is made with available experimental data and possible refinements of the present potential surface are briefly discussed.