An ab initio model for handling the Renner–Teller effect in tetra-atomic molecules. II. Study of the crossing of potential surfaces

Renner–Teller effect in six-atomic molecules: Ab initio investigation of the vibronic spectrum of

“…Refs. [22,23]). We hope that the perturbative approach developed in the present study will be helpful for interpreting the results of experimental investigations of spectra of linear polyatomic molecules and that the numerical results we give will motivate new experimental investigations on the spectrum of C À 6 .…”

“…Perturbative formulae were derived for a number of cases not considered by PK (particularly those involving the spinorbit coupling) [21]. In two recent studies, [22,23], it was shown that the RT effect in tetra-atomic molecules can be considered as a superposition of three most important mechanisms that violate the BO approximation, namely the vibronic coupling caused by distortion of linearity, conical intersections (like in the case of the Jahn-Teller effect [24]), and avoided crossings of potential surfaces. Finally, the model for handling the RT effect was generalized to linear molecules with arbitrary number of atoms [25] and applied to the concrete case of a five-atomic species (X 2 P u state of the C À 5 ion) [26].…”

“…The bending potential surfaces are computed at the bond lengths kept fixed at these values. According to our experience with four-and five-atomic molecules [19][20][21][22][23]26], we found it sensible to calculate only 13 points (for each of the components of the X 2 P u state, 1 2 A 0 and 1 2 A 00 ) determining the bending surface, all of them corresponding to planar nuclear arrangements (C s point group). Indeed, we have explicitly shown in our previous studies on the X 2 P u state of B 2 H þ 2 and the X 2 P state of HCCS (see, e.g.…”

Excited state corrections to looped adiabatic-to-diabatic transformation phases

“…The particular case of the acetylene molecular ion C 2 H þ 2 , with its ground state X 2 P u in the linear form, has been extensively treated, both theoretically and experimentally [26][27][28][29][30]. An interesting theoretical development was initiated by a series of papers [31][32][33][34], which considered distorted situations, such that the extremal two hydrogen atoms were bent away from the collinear axis.…”

“…The analytic result is finally assessed by comparing it to a solvable case (Section 4) and to a numerically obtained solution (Section 5). These arise from a Renner-Teller-type molecule [20][21][22][23][24][25][26][27][28][29][30], whose NACT aspects were recently considered [31][32][33][34][35][36].…”