Quantum Monte Carlo study of the MIES associated with H2 (X 1 sigma sub g (+)) and H2 (B 1 sigma sub u (+))

Initial efforts to characterize the electronically excited state of H4 that correlates in one asymptotic limit to H2(X 1 Sigma(+) sub q + H2(B1 sigma(+) sub u are described. Multiconfiguration self consistent field (MCSCF) and fixed-node quantum Monte Carlo (FNQMC) methods have been used to explore the suggested region of stability. The minimum on the excited-state potential energy surface for pyramidal geometries is found to have an isoceles base. Initial estimates of nonadiabiatic coupling matrix elements needed for the determination of lifetimes and stability are determined using normal mode distortions.