Ab - initio non-adiabatic couplings among three lowest singlet states of H3+: Construction of multisheeted diabatic potential energy surfaces

We calculate the adiabatic potential energy surfaces and non-adiabatic interactions among the three lowest singlet states (1(1)A', 2(1)A' and 3(1)A') of H-3(+) in hyperspherical coordinates for a fixed hyperradius, rho = 9 bohr as functions of hyperangles, theta (0 <= theta <= 90 degrees) and phi (0 <= phi <= 360 degrees). All ab initio calculations are performed using MRCI level of methodology implemented in quantum chemistry package, MOLPRO. The ground (1(1)A') and the first excited (2(1)A') states exhibit several conical intersections as functions of phi for theta >= 70 degrees. Subsequently, we carry out adiabatic to diabatic transformation (ADT) to obtain ADT angles for constructing single-valued, continuous, smooth and symmetric 3 x 3 diabatic potential energy matrix to perform accurate scattering calculations.