Three-Photon Absorption Spectroscopy of Diatomic Molecules
Multiphoton absorption spectroscopy has been used to study the isotopically-pure bromine (⁷⁹Br₂) and iodine monochlorides (I³⁵Cl), as well as the respective natural-abundance molecules.
Three-photon excitation spectra have been obtained under low- (ΔV = 1.0 cmˉ¹) and high- (ΔV = 0.2 cmˉ¹) resolution. High-resolution spectra were recorded using either a single tunable dye laser (3P1C) or two independently-tunable dye lasers (3P2C).
For ⁷⁹Br₂, the existence of at least three separate excited electronic states in the 6.7-7.3 eV region were confirmed. Two of these states were spectroscopically identified and shown to have ion-pair bonding. The two-photon transitions from the intermediate B state to these ion-pair states consisted of simple O, Q and S branches. The polarization effect on their transition probability indicated that these states were of O symmetry.
For isotopically-pure I³⁵Cl, an excited state in the 6.0 eV region has been identified.