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An atomic fluorescence technique has been used to observe iodine atoms under conditions of steadystate irradiation of I2 between 5000 and 6300 Å. Photodissociation quantum yields are reported for narrowband excitation at 12 wavelengths within this range. The yield exceeds 90% at both ends of this region with a minimum of 33% near 5900 Å and a subsidiary maximum of 72% at 5460 Å. These results are further resolved into contributions from direct dissociation via the A1u(3Π )← XO+g(1Σ ) and 1u(1Π )← X transitions, and a spontaneous predissociative decay, BO+u(3Π )→ 1u(1Π ). The rate for this predissociation fluctuates with v′ in a manner which accounts for the previously reported erratic behavior of the B-state lifetime. The total radiative decay rate varies smoothly but strongly with v′, implying that the B↔ X electronic transition moment attains a maximum for some internuclear distance in the region 3.0–3.2 Å.
Brewer et al. (Sat,) studied this question.