Quantum studies of the vibrations in $H3O2−$ and $D3O2−$

The vibrations of $H3O2−$ and $D3O2−$ are investigated using diffusion Monte Carlo (DMC) and vibrational configuration-interaction approaches, as implemented in the program MULTIMODE. These studies use the potential surface recently developed by Huang et al. [ J. Am. Chem. Soc. 126, 5042 (2004)]. The focus of this work is on the vibrational ground state and fundamentals which occur between 100 and $3700cm−1$⁠. In most cases, excellent agreement is obtained between the fundamental frequencies calculated by the two approaches. This serves to demonstrate the power of both methods for treating this very anharmonic system. Based on the results of the MULTIMODE and DMC treatments, the extent and nature of the couplings in $H3O2−$ and $D3O2−$ are investigated.