Absorption spectrum of Kr₂F(4 ²Γ) in the near ultraviolet and visible (335≤λ≤600 nm): Comparison with Kr ₂⁺(1(1/2)_u) measurements

Absolute photoabsorption cross sections for the lowest excited state (4 ²Γ of Kr₂F and the ground state (1(1/2)_u) of Kr₂⁺ have been measured in the visible and ultraviolet (Kr₂F: 248, 308, 335-600 nm; Kr₂⁺ : 360-500 nm). As predicted by theory, the Kr₂F spectrum is dominated by the 9 ²Γ ← 4 ²Γ band which peaks below 340 nm and correlates with the Kr₂⁺ 2(1/2)_g ← 1 (1/2)_u transition. However, Kr₂F(4 ²Γ) and Kr₂+ (1 (1/2)_u) both absorb more strongly for wavelengths beyond ∼450 nm than expected, apparently owing to a nonthennalized Kr₂⁺ vibrational distribution. Despite interference from Kr₂F stimulated emission between ∼350 and 460 nm, the experimental results show the Kr₂F(4 ²Γ) and Kr₂⁺ absorption profiles to be similar for λ≥460 nm but diverging rapidly as λ increases from 335 to 360 nm. At 360 nm, the absorption cross sections differ by a factor of 3. Contrary to theoretical expectations, the Kr₂F absolute absorption cross section is consistently smaller (typically < 40%) than that for Kr ₂⁺ which suggests that the impact of F^- on the Kr₂⁺ oscillator strengths is significant.