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

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 3Q0+ state dissociating to the excited I(2P1/2) limit is found to have a minimum of 1570 cm−1 significantly shifted to larger internuclear distances (RC–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 3Q0+ 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, 3Q0+, 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.