New Electronic Transition of Ovalene in Solid para-H2: The S1–S0 Transition with Its Origin at 19 400 cm–1

TL;DR

Researchers discovered a new electronic transition in ovalene trapped in solid para-H2, which could help identify mysterious interstellar spectral features.

Contribution

The study reports a new S1–S0 electronic transition in ovalene with a distinct origin and short fluorescence lifetime.

Findings

A new electronic transition in ovalene was observed at 19,400 cm–1 in solid para-H2.

The transition was assigned as S1–S0 based on quantum-chemical calculations and simulations.

The fluorescence lifetime of the new transition is approximately 10 ns.

Abstract

As part of our ongoing efforts to evaluate solid para-H2 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
(C32H14), a medium-sized planar PAH with D
2h
symmetry, in solid para-H2 and reassigned the previously reported
S1–S0 spectral features to the S2–S0 transition with a lifetime of ∼1.7
μs (

WeberI.,

,
J. Phys. Chem. Lett.
2024, 15, 10696
39413413
10.1021/acs.jpclett.4c02494PMC11514017). 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–1 in solid para-H2, approximately 1650 cm–1 below the previously
reported S2–S0 origin at 21 050
cm–1, and a short fluorescence lifetime of ∼10
ns. We assigned these new features to the S1–S0 transition based on quantum-chemical calculations at the
TD-B3LYP-D3BJ/6-311++G­(2d,2p) level and Franck–Condon Herzberg–Teller
simulations.

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