Photodissociation of ClN3 at 193 and 249 nm

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Abstract
Experiments directed toward elucidating the nature of fragments produced by the photodissociation of ClN3 have been performed. The utlraviolet absorption spectrum of this molecule exhibits three features between 300 and 170 nm, with λmax = 250, 205, and 170 = 5000 l mol−1 cm−1. Photolysis of ClN3 at 193 nm produces N2 and NCl fragments in both the singlet and triplet manifolds. In the singlet manifold of fragments, emission from electronically excited NCl(b 1Σ+) was observed. The NCl(b 1Σ+) molecules are also vibrationally excited, and emission from levels as high as v′ = 10 was recorded. Time resolution of the NCl(b 1Σ+) emission indicated that the higher vibrational levels were quenched by the gas mixture (∼3% ClN3 in helium) much more rapidly than the lower vibrational levels. The rate constant for quenching of the low v′ levels (v′ = 0–2) of NCl(b 1Σ+) was determined to be kQ = (1.72±0.05)×103 s−1 Torr−1; the rate constant for quenching of the higher levels (v′?8) was found to be kQ = (3.8±0.2)×104 s−1 Torr−1. The spontaneous emission rate for NCl(b 1Σ+), v′ = 0–2, was measured to be A = 1590±160 s−1. In the triplet manifold of fragments, photolysis at 193 nm produces excited N2(A 3Σ+u) metastable molecules. The presence of this species was determined from the observation of N2(C 3Πu)→(B 3Πg) emission produced by energy pooling processes, and from the excitation of NO by energy transfer from the N2 metastables. Photolysis of ClN3 produces at 193 nm excited singlet and triplet fragments with comparable probability. Photolysis at 249 nm also generates both excited singlet and triplet NCl and N2 fragments. Emission from vibrationally excited NCl(b 1Σ+) was again observed, and the initial vibrational distribution appeared to be similar to that found for photolysis at 193 nm. The yields for production of NCl(b 1Σ+) at 193 and 249 nm are approximately equal. Photolysis at 249 nm also produces N2(A 3Σ+u) fragments, although in substantially smaller yield than found at 193 nm.

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