Analytic Morse/long-range potential energy surfaces and predicted infrared spectra for CO–H2 dimer and frequency shifts of CO in (para-H2)N N = 1–20 clusters

Abstract

A five-dimensional ab initio potential energy surface (PES) for CO-H2 that explicitly incorporates dependence on the stretch coordinate of the CO monomer has been calculated. Analytic four-dimensional PESs are obtained by least-squares fitting vibrationally averaged interaction energies for vCO = 0 and 1 to the Morse/long-range potential function form. These fits to 30,206 points have root-mean-square (RMS) deviations of 0.087 and 0.082 cm(-1), and require only 196 parameters. The resulting vibrationally averaged PESs provide good representations of the experimental infrared data: for infrared transitions of para H2-CO and ortho H2-CO, the RMS discrepancies are only 0.007 and 0.023 cm(-1), which are almost in the same accuracy as those values of 0.010 and 0.018 cm(-1) obtained from full six-dimensional ab initio PESs of V12 [P. Jankowski, A. R. W. McKellar, and K. Szalewicz, Science 336, 1147 (2012)]. The calculated infrared band origin shift associated with the fundamental of CO is -0.179 cm(-1) for para H2-CO, which is the same value as that extrapolated experimental value, and slightly better than the value of -0.176 cm(-1) obtained from V12 PESs. With these potentials, the path integral Monte Carlo algorithm and a first order perturbation theory estimate are used to simulate the CO vibrational band origin frequency shifts of CO in (para H2)N-CO clusters for N = 1-20. The predicted vibrational frequency shifts are in excellent agreement with available experimental observations. Comparisons are also made between these model potentials.

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

“…The coupled‐cluster theory with single, double, and noniterative triple excitations (CCSD(T)) is a widely used supermolecular method. It has been used to generate PESs of, for example, CO 2 He, CO 2 H 2 , N 2 OHe, N 2 OH 2 , OCSHe, COHe, COH 2 , HCNHe, SO 2 H 2 , CS 2 He, CH 3 FHe, and H 2 H 2 . SAPT is also widely used to calculate potentials for He‐ and H 2 ‐contating complexes, such as, HeHe, CO 2 He, COH 2 , C 2 H 2 He, and N 2 OHe .…”

“…[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 ! )…”

Raman Vibrational Shifts of Small Clusters of Hydrogen Isotopologues

“…Since then, many theoretical studies have looked at superfluidity of parahydrogen clusters around different dopant molecules. [10][11][12][13][14] Joint experimental and theoretical work has recently allowed the first measurement of the so-called superfluid fraction of parahydrogen clusters. 15,16 In addition to this, the solid-like or liquid-like nature of parahydrogen at low temperatures, including the zero temperature limit, have been extensively studied [17][18][19][20][21][22][23][24][25][26] and discrepancies in the shape of the theoretically calculated ground state chemical potential have been discovered.…”

The Role of High Excitations in Constructing Sub-spectroscopic Accuracy Intermolecular Potential of He-HCN: Critically Examined by the High-Resolution Spectra with Resonance States

“…High-resolution infrared or microwave spectra studies of cold helium clusters or droplets doped with a single chromophore molecule have been used to probe the microscopic superfluid [13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Among the studied chromophor-He n species, carbon monoxide as a gentle probe molecule [27][28][29][30][31] with quantum solvation and microscopic superfluidity has received numerous atten-tions because of the well-known less anisotropic interaction and a relatively large rotational constant. HCN, as one of CO isoelectronic, was used as a probe to investigate the microscopic superfluid in the He nanodroplets and test the adiabatic following [32,33].…”