The Rotational Spectrum of the He–HCCCN van der Waals Complex:
A Comparison of Experiment and Theory.
Wendy Topic, Aiko Huckauf and Wolfgang Jäger
Department of Chemistry, University of Alberta, Edmonton AB T6G 2G2, Canada
A high level ab initio potential energy surface was calculated for the He–HCCCN van der Waals complex at the CCSD(T) level of theory, using aug-cc-pVTZ basis sets centered on each nucleus supplemented by bond functions. This surface has a global minimum at a T-shaped geometry with a well depth of –37.98 cm–1. Secondary minima exist at both the H- and N-bonded linearconfigurations, with depths of –29.25 cm–1 and –19.33 cm–1, respectively. Hutson's BOUND computer code1 was used to determine the energies of the bound states supported by the potential energy surface. Twelve rotational transitions were measured in the 7–26 GHz frequency region using a pulsed-nozzle Fourier-transform microwave spectrometer. Both strong a-type and weaker b-type transitions involving low-J rotational levels were observed, in accord with a T-shaped structure of the complex. In addition, the nuclear quadrupole hyperfine structures due to the presence of 14N (I = 1) were resolved and analyzed. The quality of the ab initio potential energy surface is evaluated by comparison of the experimental transition frequencies with those from the bound state calculations.
1 J. M. Hutson, BOUND computer code, version 5 (1993), distributed by Collaborative Computational Project No. 6 of the Science and Engineering Research Council (UK).