Photodynamics of Renner–Teller rovibronic coupling within a mixed parallel–perpendicular polarization manifold

Abstract

The Renner–Teller (RT) effect, arising from the breakdown of the Born–Oppenheimer approximation in linear molecules, couples degenerate electronic states with rovibrational motion, profoundly influencing molecular photodynamics. I present a rigorous time-dependent wavepacket formulation to describe RT rovibronic coupling between the 21A′ and 21A″ excited states of N2O within a mixed parallel–perpendicular polarization manifold. Using Jacobi coordinates, parity-adapted rovibronic basis functions, and Clebsch–Gordan expansions, I derive explicit expressions for initial wavepackets and propagate them on high-level multireference configuration interaction potential energy surfaces. This formulation captures state-specific decay and nuclear flux transfer between the coupled electronic surfaces, incorporating parity selection rules, angular momentum couplings, and symmetry-dependent dipole transitions. Application to N2O photodissociation reveals that RT coupling mediates Feshbach-type resonances, generates diffuse absorption features, and drives coupled bending–stretching dynamics that enhance low-energy spectral intensities. The methodology provides a broadly applicable framework for modeling RT-mediated rovibronic interactions in small polyatomic systems.