The N2H+–He intermolecular potential energy surface: A vibrational adiabatic correction

Abstract

This paper presents a method for constructing computationally cheap adiabatically corrected ab initio potential energy surfaces (PES) for intermolecular vibrational states. The approach reasonably reproduces previously published experimental data for the N2H+–He complex in the ground and excited intramolecular vibrational states. A comparison made between a set of intermolecular PES’s with the N2H+ core frozen into the equilibrium geometry and a set where the N–H+ stretch is averaged demonstrates the importance of including this motion. This is also reflected in a considerable improvement in the agreement between the experimental and the calculated intermolecular bending and stretching frequencies and the origin red shift (νb,calc=117.9 cm−1, νs,calc=165.2 cm−1, Δνcalc=−93.0 cm−1). A comparison is also made between the Born–Oppenheimer angular radial separation (BOARS) angular average of the adiabatically corrected PES and the previously published rotational Rydberg–Klein–Rees (RRKR) PES. The results indicate that the two-dimensional νNH=1 PES has a qualitatively correct well depth and dissociation energy (De=684.7 cm−1; D0=433.6 cm−1).