Intermolecular interaction potentials for the Ar–C2H2, Kr–C2H2, and Xe–C2H2 weakly bound complexes: Information from molecular beam scattering, pressure broadening coefficients, and rovibrational spectroscopy

Abstract

Integral cross sections and pressure broadening coefficients have been measured for the acetylene-krypton complex, by molecular beam scattering and by high resolution IR spectroscopy, respectively. A new potential energy surface ͑PES͒ is proposed to describe structure and dynamical properties of this prototypical weakly bound complex. The PES has been parametrized exploiting a novel atom-bond pairwise additive scheme and has been fitted to the experimental data. A similar PES has been obtained for the acetylene-xenon system by a proper scaling of the interaction parameters of the krypton case, based on empirical considerations. These PESs together with that recently proposed by the same authors ͓J. Phys. Chem. 109, 8471 ͑2005͔͒ for the acetylene-argon case have been employed for close coupling calculations of the pressure broadening cross sections and for a characterization of the rovibrational structure of the complexes.

Experimental 2CH excitation in acetylene-containing van der Waals complexes

“…There seems to be only one published, empirical potential energy surface (PES) for C 2 H 2 -Kr and C 2 H 2 -Xe [65], and no ab initio one until recently [40]. There are no previously reported spectral data for these species, in any spectral range.…”

“…C 2 H 2 -Ar presents a so-called pathologically flat potential energy surface, which has been extensively investigated by ab initio calculations [40,[52][53][54][55][56][57][58][59][60][61][62][63][64][65][66], demonstrating the skew T-shaped equilibrium geometry, with e ¼ 60…”

“…There are also microwave [77], and molecular beam scattering, pressurebroadened cross section data [65]. We searched for the 2CH acetylenic excitation band in Ne-HCCH using FANTASIO(þ), optimizing a mixture of argon and neon as carrier gas.…”

Line broadening and shift coefficients of acetylene at 1550nm

“…Studies of acetylene in particular have become important test cases for assessing the suitability of various models of pressure broadening [1][2][3][4][5][6][7]. Broadening and shifting of acetylene by the noble gases has become an important touchstone for testing the reliability of models of pressure-dependent line profiles, while experimental broadening and shift coefficients of acetylene by air, nitrogen, and hydrogen are essential for atmospheric monitoring of the Earth, Titan, and the Jovian planets respectively.…”

Line broadening coefficient calculations for methane perturbed by nitrogen

“…To our knowledge, theories that include such refinments were developed for simple molecular systems, and in any case not for non-linear molecules like methane as the absorber. Anyway, it seems that practical calculations are only tractable for linear molecules up to now [90][91][92][93][94]. Further investigations on these points are obviously needed.…”