Jet-Cooled Phosphorescence Excitation Spectrum of the T1(n,π∗) ← S0 Transition of 4H-Pyran-4-one

Published

April 17, 2023

Author(s)

Sean Parsons, Hucek Devon, mMishra Piyush, David Plusquellic, Timothy Zwier, Stephen Drucker

Abstract

The 4H-pyran-4-one (4PN) molecule is a cyclic conjugated enone with spectroscopically accessible singlet and triplet (n,π∗) excited states. Vibronic spectra of 4PN provide a stringent test of electronic-structure calculations. We report here the T1(n,π∗)←S0 phosphorescence excitation spectrum of 4PN, recorded under the cooling conditions of a supersonic free-jet expansion. The jet coooling has eliminated congestion appearing in previous room-temperature measurements of the T1 ← S0 band system and has enabled us to determine precise fundamental frequencies for seven vibrational modes of the molecule in its T1(n,π∗) state. We have also analyzed the rotational contour of the 000 band, obtaining experimental values for spin-spin and spin-rotation constants of the T1(n,π∗) state. We used the experimental results to test predictions from two commonly used computational methods, equation-of-motion excitation energies with dynamical correlation incorporated at the level of coupled cluster singles doubles (EOM-EE-CCSD) and time-dependent density functional theory (TDDFT). We find that each method predicts harmonic frequencies within a few percent of observed fundamentals, for in-plane vibrational modes. However, for out-of-plane modes, each method has specific liabilities that result in frequency errors on the order of 20-30%. The calculations have helped to identify a perturbation from the T2(π,π∗) state that leads to unexpected features observed in the T1(n,π∗)← S0 origin-band rotational contour.

Citation

Journal of Physical Chemistry A

Volume

127

Issue

16

Pub Type

Journals

Download Paper

https://doi.org/10.1021/acs.jpca.3c01059

Local Download

Keywords

Triplet state, Phosphorescence excitation spectrum, jet-cooled, EOM-EE-CCSD theory, rotational contour

Citation

Parsons, S. , Devon, H. , Piyush, M. , Plusquellic, D. , Zwier, T. and Drucker, S. (2023), Jet-Cooled Phosphorescence Excitation Spectrum of the T1(n,π∗) ← S0 Transition of 4H-Pyran-4-one, Journal of Physical Chemistry A, [online], https://doi.org/10.1021/acs.jpca.3c01059 , https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=936476 (Accessed March 19, 2025)