Quantification of the 248 nm Photolysis Products of HCNO (Fulminic Acid)

Abstract

IR diode laser spectroscopy was used to detect the products of HCNO (fulminic acid) photolysis at 248 nm. Five product channels are energetically possible at this photolysis wavelength: O + HCN, H + (NCO), CN + OH, CO + NH, and HNCO. In some experiments, isotopically labeled (18)O2, (15)N(18)O and C2D6 reagents were included into the photolysis mixture in order to suppress and/or isotopically label possible secondary reactions. HCN, OC(18)O, C(18)O, NCO, DCN, and NH molecules were detected upon laser photolysis of HCNO/reagents/buffer gas mixtures. Analysis of the yields of product molecules leads to the following photolysis quantum yields: ϕ1a (O + HCN) = 0.39 ± 0.07, ϕ1b (H + (NCO)) = 0.21 ± 0.04, ϕ1c (CN + OH) = 0.16 ± 0.04, ϕ1d (CN + NH(a(1)Δ)) = 0.19 ± 0.03, and ϕ1e (HNCO) = 0.05 ± 0.02, respectively. The uncertainties include both random errors (1σ) and consideration of major sources of systematic error. In conjunction with the photolysis experiment, the H + HCNO reaction was investigated. Experimental data demonstrate that this reaction is very slow and does not contribute significantly to the secondary chemistry.

Product channels in the 193-nm photodissociation of HCNO (fulminic acid)

“…Many secondary reactions following the photolysis can therefore occur. Most but not all of this secondary chemistry is identical to that considered in our previous study [8]:…”

“…3) × 10 -11 cm 3 molecule -1 s -1 and k 6 ≤ 2.1 × 10 -13 cm 3 molecule -1 s -1 at 298 K. While the rate of H + HCNO, reaction (7), is not 6 experimentally known, our previous study [8] showed that it was too slow to affect the results of HCNO photolysis experiments. Reactions (2)-(5) are fast and may produce some of the same product molecules as those probed in these experiments, potentially complicating the interpretation of product yields.…”

“…The experimental apparatus was described in our previous study [8]. Briefly, HCNO was photolyzed by 193 nm light from an excimer laser (Coherent, Compex-pro).…”

“…HCNO samples were synthesized as previously described [8,[12][13][14] 1,2,3 by flash vacuum pyrolysis of 3-phenyl-4-oximino-isoxazol-5(4H)-one. Sample purity was characterized by FT-IR spectroscopy via a strong HCNO absorption band at 2195 cm -1 [15], and a strong HNCO band at 2168 cm -1 [16].…”

“…HCNO (fulminic acid) is the less stable isomer of isocyanic acid; the kinetics of several reactions involving HCNO has only recently been studied [3][4][5][6][7]. There is only one previous study of the photochemistry of HCNO, an infrared laser spectroscopic study from our laboratory that identified five separate photolysis channels in the 248 nm photodissociation of this molecule [8].…”