The D′ → A′ Transition in IBr: A Deperturbation Analysis

The D′2( 3 P 2) → A′2( 3Π) transition in IBr occurs with maximum intensity near 3850 Å when mixtures of I 2 and Br 2 in Ar are excited by a Tesla coil. Spectra are recorded photographically for I 79Br and I 81Br separately, and 24 v′- v″ bands spanning v′ = 0-5 and v″ = 11-17 are rotationally analyzed, yielding ∼3000 line assignments. Together with existing high-quality data covering the high- v′, low- v″ region, these data are analyzed through a deperturbation model which assumes that minor anomalies in the D′-state rotational constants are the result of weak interactions with the nearby β1( 3 P 2 state. This fit pins down the absolute energies of both states for the first time, yielding T e′ = 39 457(4) cm −1, T e″ = 11 437 (4) cm −1. Other primary spectroscopic constants (cm −1) are Δ T e = 28 019.22 ω′ e = 123.064, ω e x′ e = 0.2812, B′ e = 0.02860, ω″ e = 147.631, ω e x″ e = 1.260, B″ e = 0.04290, R′ e = 3.4806 Å, R″ e = 2.842 Å.