Abstract
Water borane (BHOH) and borinic acid (BHOH) have been proposed as intermediates along the pathway of hydrogen generation from simple reactants: water and borane. However, the vibrational spectra for neither water borane nor borinic acid has been investigaged experimentally due to the difficulty of isolating them in the gas phase, making accurate quantum chemical predictions for such properties the most viable means of their determination. This work presents theoretical predictions of the full rotational and fundamental vibrational spectra of these two potentially application-rich molecules using quartic force fields at the CCSD(T)-F12b/cc-pCVTZ-F12 level with additional corrections included for the effects of scalar relativity. This computational scheme is further benchmarked against the available gas-phase experimental data for the related borane and HBO molecules. The differences are found to be within 3 cm for the fundamental vibrational frequencies and as close as 15 MHz in the and principal rotational constants. Both BHOH and BHOH have multiple vibrational modes with intensities greater than 100 km mol, namely and in BHOH, and , , , , and in BHOH. Finally, BHOH has a large dipole moment of 4.24 D, which should enable it to be observable by rotational spectroscopy, as well.
Highlights
In the case of borane, the largest difference occurs in ν3 with a deviation of only 1.9 cm−1, and the mean absolute error (MAE) or unsigned averaged deviation across the three modes is 1.1 cm−1
F12-TZ-cCR still has the slight edge with an MAE of 2.8 cm−1
Such performance indicates that both F12-TZ and F12-TZ-cCR can adequately handle the vibrational spectra of these two molecules, but for a slight increase
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. This method utilizes CCSD(T)-F12b with the cc-pCVTZ-F12 basis set, explicit treatment of core electrons, and the same correction for scalar relativity as CcCR It offers more accurate rotational constants with agreement on the order of 7.5 MHz with experimental data while still capturing an order-of-magnitude decrease in the computational cost relative to CcCR [28]. Kawaguchi et al have reported high-resolution vibrational frequencies for borane [29], and Kawashima et al have determined both rotational and vibrational experimental data for HBO [30] In both cases, these data will help to benchmark the accuracy of the theoretical results presented on the structurally similar water borane and borinic acid molecules. Borinic acid has some available rotational constants [31] that will further help to contextualize the rotational data reported here, as well
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