Vacuum ultraviolet laser spectroscopy. II. Spectra of Xe2 and excited state constants

Abstract

Vibrationally and isotopically resolved fluorescence excitation spectra of Xe₂ at 1300, 1485, and 1500 Å have been obtained and analyzed. They correspond to electronic transitions from the van der Waals ground state to the three lowest excited states. Molecules of Xe₂ were formed in the v‘=0 level of the ground state using a pulsed supersonic jet, and fluorescence emission was excited by a tunable, coherent, and monochromatic source of vacuum ultraviolet radiation generated by four‐wave‐sum‐mixing in Mg and Zn vapors. For each of the three band systems, unambiguous assignment of upper‐state vibrational quantum numbering was possible, resulting in the determination of accurate upper‐state spectroscopic constants for the first time. From system I (at ∼1500 Å) with bands v’=36 to 43, constants for the A1_u state of ^129,132Xe₂ were found to be T^’_e =63 089.9(6.9), ω_e =137.48(34), ω_ex^’_e =1.1668(43), and D_e =4174.4(7.5) cm⁻¹. Band system II (at ∼1485 Å) with bands v’=35 to 46, gave constants for the B0⁺_u state: T^’_e =63 795.6(4.2), ω_e =124.85(20), ω_ex^’_e =0.9372(24), and D_e =4446.3(5.2) cm⁻¹. Finally, system III (at ∼1300 Å) and bands v’=16 to 27 yielded the following constants for the C0⁺_u state: T^’_e =75 881.7(1.5), ω_e =49.71(10), ω_ex^’_e =0.4222(41), and D_e =1500.0 (3.4) cm⁻¹. Potential curves based on these constants were calculated for all three excited states.