Accurate quantum mechanical study of the Renner-Teller effect in the singlet CH2

Abstract

The Renner-Teller (RT) effect between the two low-lying electronic states of singlet CH(2), ã(1)A(1) and b̃(1)B(1), is studied using the multi-configuration time-dependent Hartree method with complete treatment of the RT terms. The RT terms, which are the matrix elements of the electronic orbital angular momentum operators, are calculated with ab initio methods and fitted to analytical functions. The ro-vibronic energy levels with complete treatment and constant approximation of the RT terms are calculated and compared. The influences of the geometry dependence of the RT terms on the ro-vibronic energy levels are discussed. The differences of the variation trends and influences of the RT terms between CH(2) and NH(2) are explored. In particular, as the molecule bends from linearity, the curve of the RT term (<linear span>ã(1)A(1)|L(z)(2)|ã(1)A(1)(<linear span>) first goes down to reach a minimum and then goes up leading to decreased zero point energy and bending energy levels for the lower state of CH(2) in contrast to the case of NH(2).