Calculated rovibrational energy levels and infrared spectrum of He-C₂H₂

Abstract

Accurate calculations of the energies of all bound rovibrational states, of the energies and lifetimes of some metastable states, and of the resulting rovibrational spectrum are performed for the helium-acetylene Van der Waals complex using an iterative secular equation method. The calculations are carried out both on an empirical potential surface which has a single 'T shaped' minimum, and on a potential surface based on ab initio electronic structure calculations which has a single minimum at a linear geometry. The two surfaces differ in the strength of the anisotropy, as well as its sign. A comparison of the spectra generated by the two surfaces allows spectroscopic manifestations of the shape of the potential energy surface to be discerned, results which should help guide analyses of the spectra of similar very weakly bound complexes.

A reliable new three-dimensional potential energy surface for H2–Kr

“…59. 60, which is essentially exact and has been used in a study of He-C 2 H 2 and in the determination of accurate potential energy surfaces from spectroscopic data for He-CO. 10,11,61 However, the ISE method has never previously been used to simulate hyperfine transitions, and in the He-CO work, 10,11 the partial derivatives of level energies with respect to potential function parameters required by the least-squares procedure were determined by differences, a relatively tedious procedure. The present work therefore uses the "iterative secular equation" ͑ISE͒ method of Ref.…”

Ar-C2H2 van der Waals Dimer: A Pathologically Flat Potential Energy Surface

“…[10][11] By contrast with the observation of "T"-shaped structures for Ar-C2H2 and Ar-CC>2, the linear configuration of He-C2H2 is the global minimum (according to an ab initio calculation12) and the C20 structure lies higher in energy, though a model potential suggested that the reverse is true. 12 The former result would suggest that the smaller helium atom is more sensitive to what (small) anisotropies there are in the acetylene potential than is the argon atom.…”

Microwave spectroscopic investigation of the Ne–acetylene van der Waals dimer

“…Intermolecular interactions between acetylene and rare gas atoms have been extensively investigated using high resolution spectroscopy, [3][4][5][6][7][8][9][10] scattering techniques, [11][12][13][14] and ab initio methods. 9,[15][16][17][18][19][20][21] The Ar-acetylene van der Waals dimer is the one most extensively studied. It was first studied by DeLeon and Muenter, using the molecular beam electric resonance technique.…”

“…Besides the studies on Ar-acetylene, there are also a few ab initio intermolecular potentials reported for the He-acetylene system. Slee et al constructed a potential energy surface at the MP2 level, 16 which failed to explain the recorded infrared spectrum. 23 More recently, a SAPT potential energy surface for He-HCCH was constructed by Moszynski et al 18 It shows that acetylene behaves as an essentially free internal rotor.…”