Potential energy surfaces for ground and excited electronic states of the CF3I molecule and their relevance to its A-band photodissociation

Abstract

The multireference spin–orbit (SO) configuration interaction (CI) method in its Λ-S contracted SO-CI version is employed to calculate two-dimensional potential energy surfaces for the ground and low-lying excited states of CF₃I relevant to its photodissociation in the lowest absorption band (A band). The computed equilibrium geometry for the A₁ ground state and vibrational frequency ν₃ for the C–I stretch mode agree well with available experimental data. The ³Q_0⁺ state dissociating to the excited I(²P_1/2) limit is found to have a minimum of 1570 cm⁻¹ significantly shifted to larger internuclear distances (R_C–I = 5.3 a₀) relative to the ground state. Similar to the CH₃I case, this makes a single-exponent approximation commonly employed for analysis of the CF₃I recoil dynamics unsuitable. The 4E(³A₁) state possessing an allowed transition from the ground state and converging to the same atomic limit as ³Q_0⁺ is calculated to lie too high in the Franck–Condon region to have any significant impact on the A-band absorption. The computed vertical excitation energies for the ³Q₁, ³Q_0⁺, and ¹Q states indicate that the A-band spectrum must lie approximately between 31 300 and 45 200 cm⁻¹, i.e., between 220 and 320 nm. This result is in very good agreement with the measured absorption spectrum.