Two-photon spectroscopy of atoms and molecules

Two-photon spectroscopy has become an important scientific technique. In order for two-photon spectroscopy to become more fully utilized, parameters, such as the two-photon rate constant, need to be measured so that researchers will know how large their two-photon signal will be. In this work, the target species was excited by a photon of fixed wavelength and a visible photon of tunable wavelength to a two-photon allowed transition state. The excited species was then completely ionized by an additional photon. The ion pair was detected. Not only was the two-photon rate constant measured but also the spectra were recorded by tuning the visible photon wavelength.

Argon, krypton, and molecular hydrogen (H2) were studied in a high pressure cell using parallel plate detection of the photoelectrons. Nitric oxide (NO) and the van der Waals molecule ArNO were studied using a molecular beam from a pulsed nozzle and detection of the parent ion with a quadrapole mass spectrometer. The fixed wavelength photon used with NO and ArNO was the third harmonic (355 nm) of a Nd:YAG laser. In the experiments with Ar, Kr, and H2, the third harmonic of the Nd:YAG laser was tripled in xenon to yield a vacuum ultraviolet fixed wavelength photon (118 nm).