New Electronic Transition of Ovalene in Solid para-H(2): The S(1)-S(0) Transition with Its Origin at 19 400 cm(-1).

As part of our ongoing efforts to evaluate solid -H as a matrix host for electronic spectroscopy and to explore its potential in identifying carriers of the diffuse interstellar bands (DIBs), we previously reported the electronic spectrum of ovalene (CH), a medium-sized planar PAH with symmetry, in solid -H and reassigned the previously reported S-S spectral features to the S-S transition with a lifetime of ∼1.7 μs (Weber, I., 2024, 15, 10696). Extending our investigation to lower energies, we now report a second set of spectral features, previously unobserved, with a prominent origin band at ∼19 400 cm in solid -H, approximately 1650 cm below the previously reported S-S origin at 21 050 cm, and a short fluorescence lifetime of ∼10 ns. We assigned these new features to the S-S transition based on quantum-chemical calculations at the TD-B3LYP-D3BJ/6-311++G(2d,2p) level and Franck-Condon Herzberg-Teller simulations.