Intermolecular rovibrational states of the H2O–CO2 and D2O–CO2 van der Waals complexes

Abstract

We present quantum five-dimensional bound-state calculations of the fully coupled intermolecular rovibrational states of H2O–CO2 and D2O–CO2 van der Waals (vdW) complexes in the rigid-monomer approximation for the total angular momentum J values of 0, 1, and 2. A rigid-monomer version of the recent ab initio full-dimensional (12D) potential energy surface of H2O–CO2 [Q. Wang and J. M. Bowman, J. Chem. Phys. 147, 161714 (2017)] is employed. This treatment provides for the first time a rigorous and comprehensive description of the intermolecular rovibrational level structure of the two isotopologues that includes the internal-rotation tunneling splittings and their considerable sensitivity to rotational and intermolecular vibrational excitations, as well as the rotational constants of the two vdW complexes. Two approaches are used in the calculations, which differ in the definition of the dimer-fixed (DF) frame and the coordinates associated with them. We demonstrate that with the approach introduced in this work, where the DF frame is fixed to the CO2 moiety, highly accurate results are obtained using significantly smaller basis sets in comparison to those for the alternative approach. In addition, the resulting wavefunctions tend to lend themselves better to physical interpretation and assignment. The H2O–CO2 ground-state internal-rotation tunneling splittings, the rotational transition frequencies, and the rotational constants of both vdW complexes are in excellent agreement with the experimental results. The calculated intermolecular vibrational fundamentals agree well with the scant terahertz spectroscopy data for these complexes in cryogenic neon matrices.

Photochemistry of phosphenic chloride (ClPO2): isomerization with chlorine metaphosphite (ClOPO) and reduction by carbon monoxide

“…Weakly bound complexes consisting of small molecules ( e.g. , N 2 O, 51 H 2 O, 52 and BF 3 53 ) and carbon oxide (CO or CO 2 ) are of long-standing interest, since they are transient intermediates in atmospheric and interstellar chemistry. 54 As indicated by the shifts of the IR frequencies for ClPO 2 (Table 1) and ClPO (Table S3, ESI†) in CO-matrices in comparison with the values observed in Ar-matrices, molecular complexes are expected to be formed during the bimolecular reaction of ClPO 2 + CO → ClPO + CO 2 .…”

Infrared Spectra of the Water–CO2 Complex in the 4.3–3.6 μm Region and Determination of the Ground State Tunneling Splitting for HDO–CO2

“…There have been a few theoretical ab initio calculations of the full (5D or higher) water–CO 2 potential energy surface, most recently those by Makarewitz, by Wheatley and Harvey, and by Wang and Bowman . The latter surface has been used by Felker and Bačić for detailed calculations of H 2 O– and D 2 O–CO 2 tunneling, rotational, and intermolecular vibrational energies. The calculated depth of the potential surface minimum ( D e ) is around 1050 cm –1 , and the H 2 O–CO 2 dissociation energy ( D 0 ) is about 770 cm –1 .…”

Noncovalently bound molecular complexes beyond diatom–diatom systems: full-dimensional, fully coupled quantum calculations of rovibrational states

“…1–5 A more sophisticated vibrationally adiabatic treatment was developed and implemented for (H 2 O) 2 , 6 allowing the inclusion of the monomer flexibility in an approximate manner when computing the intermolecular vibrational eigenstates. The rigid-monomer approach continues to be used widely, as illustrated by just a small sample of recent papers dealing with the rovibrational states of H 2 O/D 2 O–CO 2 , 7 (NH 3 ) 2 , 8 H 2 O–HF, 9,10 HCS + –H 2 , 11 and CH 4 –H 2 O. 12,13…”