Local nonadiabatic coupling effects on rovibrationally resolved photodissociation dynamics of BeH in ultraviolet region

Accurate photodissociation cross sections of beryllium monohydride (BeH) have been calculated for photon wavelengths ranging from 82 nm to the dissociation threshold, covering transitions from the ground state $1{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}$ to excited electronic states up to $6{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}$ and $5{\phantom{\rule{0.16em}{0ex}}}^{2}\mathrm{\ensuremath{\Pi}}$. Particular emphasis is placed on elucidating the nonadiabatic coupling between states $2{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}$ and $3{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}$, and its fundamental role in photodissociation dynamics. By explicitly incorporating these nonadiabatic effects into rovibrationally resolved cross sections calculated at various temperatures, we demonstrate how nonadiabatic couplings profoundly influence molecular fragmentation pathways. Our analysis reveals that such couplings induce numerous Feshbach resonances, significantly modifying both resonance positions and intensities in the computed cross sections. The physical origin of these resonances is interpreted in terms of coupling-induced trapping of continuum states by bound or quasibound rovibrational levels, highlighting the importance of rigorous nonadiabatic treatments for accurate predictions. This study presents the first comprehensive theoretical characterization of BeH photodissociation including nonadiabatic interactions, providing essential benchmark data for experimental verifications and astrophysical modeling, particularly relevant for understanding BeH photochemical processes in the early universe and ultraviolet-irradiated interstellar environments. The present framework provides a potentially instructive reference for future implementations of local nonadiabatic coupling in molecular photodissociation investigations.