Photochemistry of Formaldoxime−Nitrous Acid Complexes in an Argon Matrix: Identification of Formaldoxime Nitrite

Abstract

We have studied the structure and photochemistry of the formaldoxime−nitrous acid system (CH2NOH−HONO) by help of FTIR matrix isolation spectroscopy and ab initio methods. The MP2/6-311++G(2d,2p) calculations show stability of six isomeric CH2NOH···HONO complexes. The FTIR spectra evidence formation of two hydrogen bonded complexes in an argon matrix whose structures are determined by comparison of the experimental spectra with the calculated ones for the six stable complexes. In the matrix there is present the most stable cyclic complex with two O−H···N bonds; a strong bond is formed between the OH group of HONO and the N atom of CH2NOH and the weaker one between the OH group of CH2NOH and the N atom of HONO. In the other complex present in the matrix the OH group of formaldoxime is attached to the OH group of HONO forming an O−H···O bond. The irradiation of the CH2NOH···HONO complexes with the filtered output of the mercury lamp (λ > 345 nm) leads to the formation of formaldoxime nitrite, CH2NONO, and its two isomeric complexes with water. The main product is the CH2NONO···H2O complex in which water is hydrogen bonded to the N atom of the C═N group. The identity of the photoproducts is confirmed by both FTIR spectroscopy and MP2 or QCISD(full) calculations with the 6-311++G(2d,2p) basis set. The intermediate in this reaction is iminoxyl radical that is formed by abstraction of hydrogen atom from formaldoxime OH group by an OH radical originating from HONO photolysis.

OH-Induced Oxidative Cleavage of Dimethyl Disulfide in the Presence of NO

“…There is additional evidence that strongly confirms the formation of CH 3 SONO in the studied matrixes. First, as shown in Table , the identified ν(NO) wavenumber of cis -methylsulfonyl nitrite and its 15 N shift match well the corresponding wavenumbers and 15 N shifts of peroxynitrites , and nitrites. ,− Second, the band identified at 1064.0 cm –1 is tentatively assigned to CH 3 SO • , which is a substrate for the CH 3 SONO product. The SO stretching mode of CH 3 SO • was recently identified at 1071 ± 1 cm –1 in the gas phase by the time-resolved Fourier transform infrared absorption technique; it was the only mode identified for this radical.…”

“…The calculations performed for CH 3 SONO confirmed this hypothesis. It has to be remembered that ammonia is also present in the matrixes as contamination; however, being trapped in a different matrix cage from the DMDS···HONO complex, it does not participate in the matrix photochemistry as demonstrated in our earlier studies on CO/HONO/Ar, CH 2 NOH/HONO/Ar, and CH 3 SH/HONO/Ar systems …”

“…The calculations performed for CH 3 SONO confirmed this hypothesis. It has to be remembered that ammonia is also present in the matrixes as contamination; however, being trapped in a different matrix cage from the DMDS···HONO complex, it does not participate in the matrix photochemistry as demonstrated in our earlier studies on CO/ HONO/Ar, 24 CH 2 NOH/HONO/Ar, 56 and CH 3 SH/HONO/ Ar systems. 25 The DFT/B3LYP/aug-cc-pVTZ calculations revealed that the CH 3 SONO molecule can adopt two stable structures, namely cis and trans isomers ( Figure S8, Supporting Information).…”

The OH-Initiated Oxidation of CS2in the Presence of NO: FTIR Matrix-Isolation and Theoretical Studies

“…When the matrix is subjected to λ > 345 nm radiation the bands due to the CS 2 ···HONO complexes gradually diminish, and, in addition, the bands due to HONO also slightly diminish. Simultaneously, the bands characteristic for the primary and secondary HONO photolysis products appear, NO, NO 2 , N 2 O 3 , H 2 O, that were reported earlier. ,− However, we did not observe the band due to the OH free radical that was observed in our earlier study. ,, This is perhaps because most of the HONO present in the matrix interacts with CS 2 and the OH radicals formed during complex photolysis react immediately with CS 2 . Our earlier studies suggest that OH originating from HONO monomer photolysis, similarly like the OH radicals formed in H 2 O 2 photolysis, can escape the matrix cage .…”