Pyran-4-one (4H-pyran-4-one, γ-pyrone) is a prototypical α,β-unsaturated carbonyl compound. Its electronic structural characteristics make it an attractive candidate for testing computational predictions of excited-state properties. We report harmonic vibrational frequencies for the S1(n,π*) state of pyran-4-one, determined using several excited-state computational techniques, including TD-DFT, CIS(D), and EOM-EE-CCSD. We used the calculations to interpret a room-temperature S1(n,π*) ← S0 (1A2 ← 1A1) absorption spectrum of pyran-4-one appearing in the literature. Results from the EOM-EE-CCSD calculation (the highest-level ab initio method considered) suggest reassignment of several vibronic spectral features previously reported. To clarify the assignments further, we recorded the S1(n,π*) ← S0 spectrum of pyran-4-one under jet-cooled conditions, using resonant two-photon ionization (R2PI) spectroscopy. The jet cooling eliminates spectroscopic congestion arising from vibronic hot bands. We report here updated vibronic assignments in the S1(n,π*) ← S0 spectrum, including corrections to those previously reported, as well as additional bands made observable via jet cooling. We use the updated assignments to evaluate the accuracy of computed harmonic-frequency predictions of pyran-4-one in its S1(n,π*) excited state.

Spectroscopic and computational investigation of pyran-4-one in its S1(n,π*) excited state

254th National Meeting (2017)

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