Vacuum ultraviolet laser spectroscopy. V. Rovibronic spectra of Ar2 and constants of the ground and excited states

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Abstract
Vibronic spectra of three band systems of 40Ar2 and 36Ar40Ar at 108, 107, and 105 nm were recorded and analyzed. Isotope shifts of bandheads were used to establish vibrational numbering of the observed bands. Rovibronic structure was examined at resolving powers up to 5×105, yielding band centers, rotational constants, and providing evidence of Hund’s case (c) coupling for Ar2. From band system II at 107 nm, with bands involving v’=20–27 and v‘=0–5, improved constants for the ground X 0+g state were obtained: ω‘e=30.68(8), ωex‘e=2.42(5), ωey‘e=−0.062(13), ωez‘e=0.010(2), and D‘e=99.2(10) cm−1, B‘e=0.059 65(8) cm−1, and Re=3.761(3) Å. Similarly, constants for v’=20–27 of the B 0+u were evaluated, with estimates of T’e=88 210(400) and De=5640(400) cm−1. Band system I at 108 nm, led to constants for the v’=23–30 levels of the A1u state and to estimates of T’e=87 458(500) and De=5786(500) cm−1. Analysis of band system III at 105 nm yielded new and improved data for levels v’=0–9 of the C 0+u state, including T’e=95 033.6(3), De=465.8(4), ω’e=68.16, ωexe=4.631, ωey’e=0.0479, ωeze=0.0070, and B’e=0.065 24(20) cm−1, the latter resulting in Re=3.596(5) Å. Potential energy curves based on these data were calculated for the ground and three excited states.