Photodissociation of ClN3 at 193 and 249 nm

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 nm. The shortest wavelength feature (whose maximum was not resolved) was the strongest of the three, with ε170 = 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.

Photodissociation of ClN3 at 157 nm: Theory suggests a pathway leading to cyclic N3

“…The four known and experimentally identified states, namely, X 1 AЈ͑S 0 ͒, Ã 1 AЉ͑S 1 ͒, B 1 AЈ͑S 2 ͒, and C 1 AЉ͑S 3 ͒, [9][10][11][12][13] nothing is known about the mechanism of how cyclic N 3 is formed by excitation at 157.4 nm. The four known and experimentally identified states, namely, X 1 AЈ͑S 0 ͒, Ã 1 AЉ͑S 1 ͒, B 1 AЈ͑S 2 ͒, and C 1 AЉ͑S 3 ͒, [9][10][11][12][13] nothing is known about the mechanism of how cyclic N 3 is formed by excitation at 157.4 nm.…”

“…In the present work we unambiguously pinpoint the ClN 3 excited state probed in the 157.4 nm photodissociation, and propose a complex pathway for the formation of cyclic N 3 from this excitation. 10 In order to explore potential energy surfaces and dynamics after excitation to the S 7 state, we want to use a CASSCF calculation, with the full valence space consisting of 22 electrons distributed in 16 valence orbitals ͑corresponding to 2s +2p for each N and 3s +3p for the Cl͒. 14,15 The MOLPRO 2006.1 software package has been used throughout this work.…”

Photofragment translation spectroscopy of ClN3 at 248 nm: Determination of the primary and secondary dissociation pathways

“…While this channel is not energetically accessible for 248-nm photolysis, when the photolysis wavelength is 193 nm, N 2 ͑A 3 ⌺ g + ͒, presumably from channel 5, has been detected, 6,12 along with NCl ͑b 1 ⌺ + ͒ which can be produced by a second spin-allowed channel, 6,36 …”

Photodissociation of Gaseous NCl3 at 193 and 249 nm

“…Features corresponding to the ∆V ) ( 1, (2, and +3 sequences are also evident, and their intensities indicate that the excited NCl(b 1 Σ + ) is formed with considerable vibrational excitation. 12,13 The intensity of the emission varied linearly with the fluence of the photolysis laser, suggesting that NCl(b 1 Σ + ) is produced directly by the single photon photodissociation of NCl 3 .…”