Cold-surface photochemistry of primary and tertiary alkyl nitrites

Loss of NO(g) to painted surfaces and its re-emission with indoor illumination

Heterogeneous surface reactions play a key role in the chemistry of the indoor environment because of the large indoor surface-to-volume ratio. The presence of photocatalytic material in indoor paints may allow photochemical reactions to occur at wavelengths of light that are present indoors. One such potential reaction is the heterogeneous photooxidation of NO to HONO. NO(g) is commonly found indoors, originating from combustion sources, ventilation and infiltration of outdoor air. We studied the interaction of NO(g) with painted surfaces illuminated with indoor fluorescent and incandescent lighting. There is a loss of NO(g) to painted surfaces in the dark at both 0 and 50% RH. At 50% RH, there is a re-release of some of that NO(g) under illumination. The same behavior is observed for illumination of different colored paints. This is in contrast to what is seen with TiO₂ as the substrate, where photoenhanced uptake of NO(g) and formation of NO₂ (g) are observed. We hypothesize that the loss of NO(g) is due to adsorption and diffusion into the paint. The re-release of NO under illumination is thought to be due to photooxidation of NO to HONO on the painted surface at higher relative humidities and subsequent HONO photolysis.

Direct observation of the intermediate radical in the photodissociation of 1,3-cyclohexane dinitrite

A two-step photodissociation mechanism was proposed in the literature for dinitrites in the absence of direct evidence of the intermediate species. In this work, photodissociation dynamics of cis and trans 1,3-cyclohexane dinitrites are investigated by laser-induced fluorescence (LIF) spectroscopy and theoretical calculation methods. Observation of the fluorescence spectra of the 3-nitrosooxy cyclohexoxy radical provides direct experimental evidence that the intermediate species exists. The results indicate that photodissociation of dinitrites indeed follows a two-step mechanism, i.e. one of the O-NO bonds of the molecule breaks first upon 355 nm laser photolysis and generates an alkoxy radical (RO) plus NO; the alkoxy radical further dissociates in the secondary dissociation step and produces small fragments such as vinoxy etc.

Photodissociation dynamics of dinitrite at 355 nm: initiation of a reactive pathway

Dinitrites are effective nitrosating reagents in preparative chemistry and their decomposition products are involved in the atmospheric reaction of volatile organic compounds with nitrogen oxides (NO_x). In this work, photodissociation dynamics of five alkyl dinitrites were investigated by detecting the LIF spectra of the dissociation products and theoretical calculations. The results showed that the C-C bond connecting the two nitrosooxy (-ONO) functional groups was the weakest bond in vicinal dinitrites and aldehydes were the dissociation products. For dinitrites with two ONO groups separated by a CH₂ group, vinoxy and 1-methylvinoxy radicals were detected as the fragments via photodissociation, indicating a different mechanism compared to thermal decomposition. This observation demonstrated that a new reactive pathway could be initiated by photolysis of dinitrites.