Anharmonic vibrational frequencies of ammonia borane (BH3NH3)

The fundamental vibrational frequency of the B–N stretch in BH3NH3 has eluded gas-phase experimental observation for decades. This work offers a theoretical anharmonic prediction this mode to be 644 cm−1, using Cartesian quartic force field at CCSD(T)-F12/cc-pVTZ-F12 level theory. other frequencies reported herein have mean absolute error only 5 cm−1 from seven available frequencies, making and rotational constants most accurate computational data date. inclusion Fermi, Coriolis, Darling–Dennison resonances is major source accuracy, with non-resonance-corrected having 10 cm−1. In particular, 2ν6 = ν5 type 1 Fermi resonance increases stretching by 14 compared previous work. Ammonia borane also represents one largest molecules ever studied fields, an important step extending breadth application these rovibrational techniques.