UV Photodissociation Dynamics of HN3 in 190-248 nm

Abstract

The H+N 3 channel in the ultraviolet photodissociation of HN 3 has been investigated from 190 nm to 248 nm using the high-n Rydberg H-atom time-of-flight technique. Product translational energy distributions as well as product angular anisotropy parameters were determined for the H+N 3 channel at different photolysis wavelengths. N 3 vibrational state distribution has also been derived from the product translational energy distribution at these wavelengths. Above photolysis wavelength 225 nm, HN 3 predominantly dissociate through the repulsive state. Below 225 nm, a new slow channel starts to appear at 220 nm in addition to the existing channel. This channel is attributed to a ring closure dissociation channel to produce the cyclic N 3 product. As photolysis energy increases, this new channel becomes more important.

Photodissociation Dynamics of HN3 and DN3 at 157 nm

“…The error limit is due to the uncertainty in determining the threshold, the photolysis laser line width and the resolution of the TOF spectrometer. Our present result is very close to the recent experimental value obtained by Cook et al, 14 D 0 (H-N 3 ) ) 30970 ( 50 cm -1 , and by Zhang et al, 16,17…”

“…From the translational energy distributions shown in Figure 3, the average translational energy, 〈E trans 〉 is determined to be about 35%. By comparison of this value with the recent experimental results at other photolysis wavelengths (73% at 248 nm, 64.6% at 230 nm, and 49% at 193.3 nm), 15,17 it is obvious that more available energy is deposited into the N 3 product internal energy as photolysis energy increases.…”

“…Recently, the high-n Rydberg H-atom time-of-flight (HRTOF) technique has also been employed to investigate the H-atom channel. [13][14][15][16][17] Cook et al 13,14 reported the translational energy spectra of the H + N 3 (X ˜) products for photolysis wavelengths between 240 and 280 nm. On the basis of their experimental results and ab initio potential energy surface calculations, they concluded that the N 3 fragments were formed in the progression involving both the symmetric stretch mode (ν 1 00) only and the symmetric stretch mode combined with one and two quanta of bending motion, ν 2 .…”

“…The observed product anisotropy parameter is clearly energy-dependent, implying multiple dissociation pathways are involved. More recently, Zhang et al 16,17 reinvestigated the photodissociation of HN 3 /DN 3 using the HRTOF method, spanning the range of photolysis wavelengths between 188 and 280 nm in roughly 5 nm steps. They have observed subtle yet striking changes in the photodissociation dynamics as the photolysis energy passes through ∼5.6 eV.…”

The collision-free photochemistry of methyl azide at 157 nm: Mechanism and energy release

“…Other photochemical precursors to cyclic-N 3 have also been found. Rydberg H-atom time-of-flight studies of hydrazoic acid (HN 3 ) photolysis suggest cyclic-N 3 formation, 16,17 and clear evidence is found in the near threshold VUV photoionization-based PTS measurements on methyl azide (CH 3 N 3 ) photodissociation at 193 nm. 18 A complete review is available.…”