Quantum chemical rovibrational analysis of aminoborane and its isotopologues

Abstract

Aminoborane, H2NBH2 and its isotopologues, H2N10BH2, D2NBD2, and D2N10BD2, have been studied by high‐level ab initio methods. All calculations rely on multidimensional potential energy surfaces and dipole moment surfaces including high‐order mode coupling terms, which have been obtained from electronic structure calculations at the level of explicitly correlated coupled‐cluster theory, CCSD(T)‐F12, or the distinguishable cluster approximation, DCSD. Subsequent vibrational structure calculations based on second‐order vibrational perturbation theory, VPT2, and vibrational configuration interaction theory, VCI, were used to determine rotational constants, centrifugal distortion constants, vibrationally averaged geometrical parameters and (an)harmonic vibrational frequencies. The impact of core‐correlation effects is discussed in detail. Rovibrational VCI calculations were used to simulate the gas phase spectra of these species and an in‐depth analysis of the ν7 band of aminoborane is provided. Color‐coding is used to reveal the identity of the individual progressions of the rovibrational transitions for this particular mode.

The performance of hybrid and F12∗/F12c explicitly correlated coupled cluster methods for use in anharmonic vibrational frequency computations

“…In particular for rotational constants, standard F12b-TcCR has a MAE of 482.8 MHz while the hybrid F12-TcCR+TZ has a slightly higher MAE of 488.0 MHz. Both of these MAEs are large, but they are very similar to each other and in line with previous work [48,136]. Based on relative differences as measured by the MA%E, both hybrid methods proform the same at 0.15% and better than F12b-DZ, F12b-TZ, and F12b-DcCR which have MA%Es of 0.44%, 0.45%, and 0.20%, respectively.…”

Spectroscopic Characterization of Diazophosphane—A Candidate for Astrophysical Observations

“…Again, we provide a comparison between calculations based on a PES using the frozen core approximation and a PES obtained by allelectron calculations. Since diazophosphane is a near-prolate asymmetric top molecule, it has one very large rotational constant, i.e., A, and two rather small ones being very similar in size, B and C. The relative deviation between the fc and ae results are about 0.5%, which is similar to the findings in Schneider & Rauhut (2022). Although the quartic and especially sextic constants are several orders of magnitude smaller, the relative deviations are about the same as for the rotational constants.…”

“…The first one uses the frozen core approximation relying on error compensation with respect to neglected contributions within the electronic energies and leads to vibrational frequencies that usually match nicely with experimental results. The second PES uses all-electron calculations, which have shown a better agreement for the spectroscopic constants in the past (Schneider & Rauhut 2022;Tschöpe & Rauhut 2023). To determine the vibrational and rovibrational frequencies and intensities, VCI and RVCI theory has been used.…”

“…For this reason, this approximation is often used to calculate rovibrational line lists, spectra, and partition functions. The second PES was obtained by all-electron (ae) correlation calculations, which explicitly account for core-core and core-valence interactions, since the work of Schneider & Rauhut (2022) has shown, that at least for the determination of spectroscopic constants this approach leads to slightly better results. In most of our analyses, we compare the results obtained from these two different PESs to narrow the range where experimental values could be expected.…”

Efficient vibrationally correlated calculations using n-mode expansion-based kinetic energy operators

“…dipole moments, have been used in combination with recti- and curvilinear coordinate systems. 9,10,25–28 This holds true for the KEO as well. When working with the Watson KEO, n -mode expansions have been used to treat the elements of the inverse effective moment-of-inertia tensor (commonly denoted μ αβ ).…”