Electronic Spectroscopy of Transient Molecules

The generation and characterization of transient species is a challenge for experimentalists as these species are short‐lived and reactive. Our group has focused on the measurement of the electronic spectra of unstable molecules relevant to astrophysical observations as well as to terrestrial environments. Methods of generating and collecting the electronic spectra of radicals and ions have been developed. By first using a mass‐selected matrix isolation technique, the transitions of these species are obtained in neon matrices, following which the gas‐phase transitions can be sought. To this end, an assortment of techniques is employed, for example, cavity ring‐down and frequency modulation absorption spectroscopy, degenerate four‐wave mixing, resonant multiphoton ionization, and photofragmentation schemes that utilize the cooling capabilities of an ion trap.
These gas‐phase‐based approaches are illustrated by the electronic spectra of a number of key species providing detailed information about their electronic structure, thus allowing for direct comparison between astronomical observations and theory. The studies of the carbon chains have led to interesting astrophysical implications for the systems, which could be responsible for the diffuse interstellar bands.