A comprehensive experimental and theoretical study of H2−CO spectra

Abstract

A detailed description of a new ab initio interaction potential energy surfaces for the H2-CO complex computed on a six-dimensional grid (i.e., including the dependence on the H-H and C-O separations) is presented. The interaction energies were first calculated using the coupled-cluster method with single, double, and noniterative triple excitations and large basis sets, followed by an extrapolation procedure. Next, a contribution from iterative triple and noniterative quadruple excitations was added from calculations in smaller basis sets. The resulting interaction energies were then averaged over the ground-state and both ground- and first-excited-states vibrational wave functions of H2 and CO, respectively. The two resulting four-dimensional potential energy surfaces were fitted by analytic expressions. Theoretical infrared spectra calculated from these surfaces have already been shown [P. Jankowski, A. R. W. McKellar, and K. Szalewicz, Science 336, 1147 (2012)] to agree extremely well, to within a few hundredth of wavenumber, with the experimental spectra of the para and orthoH2-CO complex. In the latter case, this agreement enabled an assignment of the experimental spectrum, ten years after it had been measured. In the present paper, we provide details concerning the development of the surfaces and the process of spectral line assignment. Furthermore, we assign some transitions for paraH2-CO that have not been assigned earlier. A completely new element of the present work are experimental investigations of the orthoH2-CO complex using microwave spectroscopy. Vast parts of the measured spectrum have been interpreted by comparisons with the infrared experiments, including new low-temperature ones, and theoretical spectrum. Better understanding of the spectra of both para and orthoH2-CO complexes provides a solid foundation for a new search of the bound H2-CO complex in space.

The CO-H2van der Waals complex and complex organic molecules in cold molecular clouds: A TMC-1C survey

“…The energy levels are labeled by quantum numbers J, parity P and n J ,P, a consecutive number of the state for the given values of J and P (see Jankowski et al 2013 for details). In both panels, the targeted transitions are indicated by arrows.…”

“…Recent laboratory studies of the CO-H 2 complex have provided precise MMW frequencies with uncertainties of about 50 kHz for the complex in different spin modifications and for its deuterated isotopologues: CO-paraH 2 (Potapov et al 2009b), CO-orthoH 2 (Jankowski et al 2013), CO-orthoD 2 (Potapov et al 2009a) and CO-HD (Potapov et al 2015). Therefore, the availability of precise rest frequencies and modern astronomical receivers (with a sensitivity several times better than the old receivers used 20 years ago), combine in a great opportunity to detect for the first time a van der Waals complex in the ISM.…”

Potential generation and path‐integral Monte Carlo in study of microscopic superfluidity

“…[44,45] SAPT is also widely used to calculate potentials for He-and H 2 -contating complexes, such as, HeAHe, [46] CO 2 AHe, [47] COAH 2 , [48] C 2 H 2 AHe, [49] and N 2 OAHe. [50] For some systems, such as COAH 2 , [35][36][37] CCSDT(Q) [51] with triple and quadruple excitations is needed to make the calculated spectroscopic transitions agree with experiment. For larger systems, for example, HCCCNAHe, [52] OCSAHe, [53,54] and OCSAH 2 , [55] less expensive many-body perturbation theory at the nth order [56] with n5224 can also be used.…”

“…The coupled-cluster theory with single, double, and noniterative triple excitations (CCSD(T)) [22,23] is a widely used supermolecular method. It has been used to generate PESs of, for example, CO 2 AHe, [24] CO 2 AH 2 , [25][26][27] N 2 OAHe, [28][29][30] N 2 OAH 2 , [31] OCSAHe, [14,32] COAHe, [33] COAH 2 , [34][35][36][37] HCNAHe, [38,39] The rotor (e.g., a stack of disks) in a) undergoes an oscillation around the vertical pivot axis at an angular frequency x. The rotor (e.g., an OCS molecule) in b) undergoes a coherent quantum rotation (indicated bŷ j ! )…”

Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms

“…This is illustrated by the depth of the well in the three-dimensional (3D) H-CO potential energy surface (PES) of Song et al, , respectively. [18][19][20][21] Another essential difference with He-CO and H 2 -CO important for inelastic collision processes is that the H-CO potential has a barrier for dissociation of HCO into H + CO with a height of 0.141 eV (1138 cm −1 ) above the H + CO limit, while He-CO and H 2 -CO have no barriers. In principle, the strong interaction in H-CO gives rise to strong vibrational coupling and highly efficient translation-vibration (T-V) energy transfer, but in order to get into the region of the deep well, the H atom approaching the CO molecule must first pass over or tunnel through the barrier.…”