High resolution studies of the vibronic coupling in sodium trimers

High resolution gas phase spectra of the sodium trimer were measured by resonant two-photon ionization spectroscopy using narrow-band continuous-wave lasers and mass-selective detection of the ions. A cold molecular beam of sodium clusters was extracted from a mixed supersonic expansion of sodium vapor and argon. The rotational temperature of the beam varies between 5 and 10 degrees Kelvin. The rotational structure of vibrational bands of the B-X system of Na...