Accidental conical intersections in H₂Cl⁺(¹A′)

Abstract

Conical intersections in C,, C?,, and linear configurations for the 'A' states of the H2C1+ molecule are investigated with the help of a 10 x 10 model Hamiltonian matrix in a valence-bond basis. The line of intersection (linen) between states 2 and 3 is traced from one end point, an intersection between two states of 'B2 symmetry in a CZv configuration, to the other end point, an intersection between two 'C+ states in a linear H-H-CI configuration. The linea consists of 5 branches having symmetries C,y, C,,, C,,,, C1,, and C,. A litzea between states 3 and 4 starting at a crossing of 'C+ and 'n states in a linear C, , configuration consists of three branches (C,r, C2", CI) leading to the asymptotic region CI + HL The starting point of linea 314 is connected to the asymptotic region H + HCI via a linen in the linear configuration. Linene of C, symmetry could be found by examining the eigenvalues of the Hessian matrix of second derivatives along a line of intersection in a higher symmetry (C2" or linear), a useful method for locating accidental intersections that lends itself readily to nD initio calculations. The existence of the litleae could be related to physical properties of the molecule, such as the dipole moment, indicating that the model Hamiltonian does reflect the true physical behaviour.PHILIP

Unanticipated confluences of seams of conical intersection: Reinvestigating intersecting potential-energy surfaces using new tools. I. C(3P)+H2

“…A discussion of united atom limits for seams of conical intersections based on semiempirical wave functions can be found in Ref. 7.…”

“…Intersecting seams can have important implications for nonadiabatic dynamics, since strong nonadiabatic effects will be encountered in unexpected regions of nuclear coordinate space. As points of conical intersection are frequently referred to as diabolical points, 6,7 we refer to points at the intersection of two seams of conical intersections as doubly diabolical points. 6 For the M-H 2 molecules noted above the seams of conical intersection consist of a readily determined C 2v symmetry-allowed portion, and a C s portion resulting from the intersection of two states of the same symmetry which could not be anticipated on the basis of point group symmetry.…”

“…However in the B-H 2 study 5 the existence of the doubly diabolical point, and hence the C s portion of the seam, was established systematically using a recently suggested algorithm 6 that employs information obtained solely from the readily anticipated C 2v portion of the seam. Previously Kuntz et al 7 had located doubly dia-bolical points in H 2 Cl ϩ using a systematic technique that exploits the computational simplicity of the semiempirical diatomics in molecules approach.…”

A comparative study of the spectroscopic features of the low-lying electronic states of H2F+ and H2Cl+ ions

“…Existence of the 1 Π u state as the first excited singlet state is also supported by other theoretical studies. [35][36][37] The 1 3 B 1 and the 1 3 A 1 states, correlate at linear geometry with the doubly degenerate 3 Π u state. Similarly, the 2 1 A 1 state shows the same geometry as the 1 1 B 1 state at the minimum energy point with σ 2 g σ 2 u π 3 u σ g as the leading configuration in the D ∞h symmetry.…”

“…Studies at SCF/6-31G**, MP2 (full)/6-31G** and MP2 (full)/TZP levels for the geometrical parameters of this ion have also been reported. 22 Multireference configuration interaction (MRCI) based approach 35 on the low-lying states and methods employing diatomicsin-molecule model, 36,37 to study the 1 A′ potential energy surfaces, are few more examples of significant work on this molecular ion in the last decade.…”