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

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.