Quantum dynamical calculation of all rovibrational states of HO₂ for total angular momentum J = 0-10

The energy levels and wavefunctions for all rovibrational bound states of HO₂ are systematically computed, for all total angular momentum values J = 0-10. The calculations are performed using ScalIT, a suite of software modules designed to enable quantum dynamics and related calculations to be performed on massively parallel computing architectures. This is the first-ever application of ScalIT to a real (and very challenging) molecular application. The codes, and in particular, the algorithms (optimal separable basis, preconditioned inexact spectral transform, phase space optimized discrete variable representation basis) are so efficient that in fact, the entire calculation can be performed on a single CPU-although parallel scalability over a small number of CPUs is also evaluated, and found to be essentially perfect in this regime. For the lowest 11 vibrational states, the rotational levels for J = 0-10 fit fairly well to a rigid rotor model, with all vibrational-state- dependent rotational constants, B_eff(v), close to values obtained from a previous calculation for J = 0 and 1 [J Chem Phys 107:2705, 1997]. However, comparatively larger discrepancies with the rigid-rotor model are found at the higher J values, manifesting in the observed K-splitting (along the O-O bond) of rovibrational levels. This supports earlier work [J Chem Phys 113:11055, 2000] suggesting that Coriolis coupling is quite important for this system.