High-resolution absorption, excitation, and microwave-UV double resonance spectroscopy on a molecular beam: S1 aniline Original Research Article

A high-resolution, molecular beam UV spectrometer was constructed that uses both traditional laser induced fluorescence and optothermal detection of the energy content of the molecular beam. Microwave-UV double resonance capabilities were implemented to assist in the assignment of the UV spectra of medium-sized molecules with the ultimate goal to unravel their S1/T1 dynamics. It is shown that high quality optothermal spectra can be obtained in the 300 nm region, by recording the high-resolution, optothermally detected, S1 ← S0 0-0 absorption spectrum of aniline with a signal-to-noise ratio comparable to that of the LIF spectrum of the same band. The latter is used to obtain accurate rotational constants for the vibrationless S1 state of this molecule. Double resonance is demonstrated by confirming several rotational assignments in this way.