Anharmonic Vibrational Frequencies of Water Borane and Associated Molecules

Water borane (BH [Formula: see text] OH [Formula: see text]) and borinic acid (BH [Formula: see text] OH) 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 [Formula: see text] for the fundamental vibrational frequencies and as close as 15 MHz in the [Formula: see text] and [Formula: see text] principal rotational constants. Both BH [Formula: see text] OH and BH [Formula: see text] OH [Formula: see text] have multiple vibrational modes with intensities greater than 100 km mol [Formula: see text] , namely [Formula: see text] and [Formula: see text] in BH [Formula: see text] OH, and [Formula: see text] , [Formula: see text] , [Formula: see text] , [Formula: see text] , and [Formula: see text] in BH [Formula: see text] OH [Formula: see text]. Finally, BH [Formula: see text] OH [Formula: see text] has a large dipole moment of 4.24 D, which should enable it to be observable by rotational spectroscopy, as well.