Calculated rotational spectrum of Ar...CO from an ab initio potential energy surface: A very floppy van der Waals molecule

Abstract

Using the ab initio potential of Shin et al. (to be published), we have calculated the bound states and infrared absorption spectrum of the van der Waals complex Ar...CO. The results show that Ar...CO cannot be treated as a quasirigid rotor, nor as a molecule with a free internal rotor. In particular, a transition to the first excited van der Waals bending level is predicted to be present in the spectrum, and its frequency varies with Ω (the projection quantum number of the total angular momentum onto the intermolecular axis going from the center of mass of CO to the Ar atom). It is also shown that, although the spectrum cannot be analyzed by the use of a rigid rotor model, rotational ‘‘constants’’ can still be defined for each value of Ω. This is consistent with the available experimental data and the predicted bending excitation can account for unassigned transitions in the infrared spectrum of this complex. Finally, a sensitivity analysis of the calculated spectrum with respect to the potential anisotropy has been performed.

On Atomic Delocalization in van der Waals Bonding: Evidence from a Stochastic Picture

“…The interesting feature of these DMC calculations is that they directly underline the dynamic nature of the structures in the two clusters and the quantum delocalisation of the He and Ar atoms within the systems. In both cases, in fact, the floppy character of the vdW complexes already pointed out in previous studies [13,16,34,35] is confirmed by the DMC results. Although the rather dubious validity of invoking a specific structure to describe the highly delocalized He ± M bound states has been mentioned before in several instances,…”

“…[34,35] For this system the variational problem of determining bound and metastable states becomes numerically more demanding than for He ± CO. [39] On the other hand, once the PES is available, the DMC evaluation of its ground bound state is not computationally more difficult than that of the He complex.…”

Rovibrational structure of the Ar–CO complex based on a novel three-dimensional ab initio potential

“…The Ar-CO complex can be considered a prototype van der Waals system, as witnessed by the extensive experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and theoretical [20][21][22][23][24][25][26][27][28][29][30][31] work on its description. For example, the first paper, published in 1978 by Parker and Pack, 20 used Ar-CO as a model system for the development of electron gas methods for calculating intermolecular potential energy surfaces ͑IPESs͒.…”

Theoretical absorption spectrum of the Ar–CO van der Waals complex

“…Due to its relative simplicity it has been widely studied both from the experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and the theoretical [20][21][22][23][24][25][26][27][28][29][30][31][32] points of view. Because of the very small dipole moment of CO, 0.109 80D, 33 Ar-CO is a challenge both from the experimental and the theoretical points of view.…”

“…Many authors have concentrated on calculating accurate intermolecular potential energy surfaces. [23][24][25][26][27][28][29][30][31][32] Although fitted to reproduce the lowest excited bending frequency, the best semiempirical potential by Jansen 24,28 allows reproduction of the higher levels. Among the most accurate ab initio intermolecular potentials is that of Toczyłowski and Cybulski, 30 obtained for a fixed CO bond distance with the coupled cluster singles and doubles including connected triples corrections method ͓CCSD͑T͔͒ and the augmented correlation consistent polarized triple zeta basis set ͑aug-cc-pVTZ͒ extended with two different sets of midbond functions (3s3p2d2 f 1g and 3s3 p2d1 f 1g).…”