Chlorocyclohexane Valence and Rydberg Electronic Excitations

Here we present new cross-section values of chlorocyclohexane (C₆H₁₁Cl) from vacuum ultraviolet (VUV) photoabsorption measurements in the photon energy range of 5.0–10.8 eV (115–248 nm). Theoretical calculations using time-dependent density functional theory (TD-DFT) have been performed to aid in the interpretation of the photoabsorption spectrum. The information from these calculations has allowed the assignment of the excited states in valence, mixed valence-Rydberg, and Rydberg transitions. The fine features in the photoabsorption bands have been assigned to (C–H₂)₄ symmetric stretching (and C–H stretching), $v_7^{\prime }\left(a^{\prime }\right)$, (C–H₂)₄ wagging, $v_{11}^{\prime }\left(a^{\prime }\right)$ and ring puckering/C–Cl stretching $v_{23}^{\prime }\left(a^{\prime }\right)$ modes. From the absolute cross-section values, photolysis lifetimes in the Earth’s atmosphere have been estimated, showing that solar photolysis may only be considered a relevant sink at altitudes above 20 km. Additional calculations at the TD-DFT level of theory have been performed to obtain potential energy curves for the lowest-lying electronic states, highlighting the role of predissociative character.