Theory of resonance Raman scattering by doubly degenerate modes

Abstract

A model is presented that allows calculation of excitation profiles, depolarization ratios, and resonance Raman spectra of doubly degenerate (e-type) modes. It consists of a doubly degenerate excited (E-type) electronic state and a nondegenerate excited A -or B -type electronic state. The sources of Raman scattering by the e-type modes are pseudo-lahn-Teller (Herzberg-Teller) interactions between these excited states and lahn-Teller and/or Renner-Teller interaction within the E-type electronic state.Molecules of trigonal, pentagonal, and hexagonal symmetries are investigated for different coupling schemes and different energy separations between the two excited states. The results are presented in the form of three-dimensional graphs for the fundamental and the first two overtones together with the corresponding absorption spectrum. The model also allows one to follow changes in resonance Raman scattering produced by trigonal distortion of molecules possessing a triply degenerate electronic state in resonance with the incident light. The case of resonance scattering in the region of a forbidden nondegenerate state which is likely to occur in hexagonal molecules such as benzene is also discussed.

Photoionization-induced dynamics of the ammonia cation studied by wave packet calculations using curvilinear coordinates

“…This study was based on a vibronic coupling model [12][13][14] that included only linear coupling terms. It included the coupling of the non-degenerate ground state with the degenerate first excited state known as the pseudo-Jahn-Teller (PJT) effect [12,[15][16][17]. Indeed, a conical intersection [18,19] between ground and excited state was found in this study and fast but incomplete decay to the ground state was predicted.…”

The Jahn–Teller and pseudo‐Jahn–Teller effects in the anion photoelectron spectroscopy of B3 cluster

“…This type of coupling is known as pseudo-Jahn-Teller (PJT) coupling in the literature. 7,11,12,[16][17][18] The existence of different types of coupling lead to the formation of multiple conical intersections of electronic states and the nuclear dynamics proceeds via highly complex nonadiabatic paths.…”

(B+E⊗b)⊗e Jahn–Teller and pseudo-Jahn–Teller effects in the spiropentane radical cation

“…The two split surfaces at the crossing points (a stable minimum in the original undistorted configuration) resemble the topology of a double cone known as ''conical intersections" (CIs) in the literature [9,10]. The pseudo-JahnTeller (PJT) effect is defined as the effect due to the vibronic coupling of a JT state with a nearby nondegenerate state or between two JT states [6,[11][12][13][14]. Such coupling leads to the formation of multiple CIs on the electronic PESs.…”

“…Such a coupling is known as PJT coupling [6,[11][12][13][14] and the effect is designated as (B + E b) e-PJT effect. The a 2 vibrational modes are not active in first-order in either electronic states.…”