THE N2H-HE INTERMOLECULAR POTENTIAL-ENERGY SURFACE - A VIBRATIONAL ADIABATIC CORRECTION()

This paper presents a method for constructing computationally cheap ad iabatically corrected ab initio potential energy surfaces (PES) for in termolecular vibrational states. The approach reasonably reproduces pr eviously published experimental data for the N2H+-He complex in the gr ound and excited intramolecular vibrational states. A comparison made between a set of intermolecular PES's with the N2H+ core frozen into t he equilibrium geometry and a set where the N-H+ stretch is averaged d emonstrates the importance of including this motion. This is also refl ected in a considerable improvement in the agreement between the exper imental and the calculated intermolecular bending and stretching frequ encies and the origin red shift (nu(b,calc)=117.9 cm(-1) nu(s,calc)=16 5.2 cm(-1), Delta nu(calc)= -93.0 cm(-1)). A comparison is also made b etween the cm Born-Oppenheimer angular radial separation (BOARS) angul ar average of the adiabatically corrected PES and the previously publi shed rotational Rydberg-Klein-Rees (RRKR) PES. The results indicate th at the two-dimensional nu(NH)=1 PES has a qualitatively correct well d epth and dissociation energy (D-e=684.7 cm(-1); D-0=433.6 cm(-1)). (C) American Institute of Physics.