Multiphoton ionization spectroscopy of acetaldehyde in its lowest Rydberg state

Publisher Website
Google Scholar
Abstract
The multiphoton ionization spectrum of acetaldehyde vapor, two photon resonant at the n→3s Rydberg transition, has been studied at 1 cm−1 resolution. Vibrational analysis shows that the molecule remains planar in the resonant state, and that the methyl group torsional barrier has a value of 755±10 cm−1 in that state, compared to 413 cm−1 in the ground state. GTO calculations in the ground state and in the lowest ionic state are only partly successful in explaining the barrier. The Rydberg nature of the resonant state has been verified by the extreme broadening of its two photon absorption when pressurized by ?80 atm of argon. Due to the near resonance of the first absorbed photon with the (n,π*) state, the multiphoton transition is extraordinarily intense; the origin band is at 55 039 cm−1, and displays a circular‐to‐linear polarization ratio varying from 0.08 to 0.8 depending upon the laser power and sample pressure.