Understanding the structure and properties of cyclohexoxy radical and its substitutes is important because of their presence in combustion processes, in atmospheric chemistry, and as intermediates in the hydrocarbon reactions. In this work, jet-cooled laser-induced fluorescence (LIF) spectra of five dimethyl substituted cyclohexoxy radicals are obtained for the first time. The correlation between the spectral variations and the radical structural changes is studied with the assistance of theoretical calculations at the B3LYP/6-31+G(d) and CASSCF/6-31+G(d) levels. The results show that the spectral characters of the dimethylcyclohexoxy radicals and their dissociation kinetics are predominantly affected by the methyl substitution position related to the C–O group. The spectral effect of the two methyl groups will add up if they locate on asymmetric carbons of the cyclohexoxy ring. Methyl substitution on β carbon weakens the six-member ring of cyclohexoxy and results in unimolecular dissociation via β C–C bond cleavage on the methyl group side and forms vinoxy variants. This study clearly shows that the LIF spectra can be used to identify cyclohexoxy and the isomers of its methyl substitutes. The results will help to understand the photochemistry of cyclic hydrocarbons in the atmospheric and combustion processes.

Spectroscopic detection is an important method to monitor alkoxy radicals in atmospheric photochemistry studies. In this work, we report the first observation of the laser-induced fluorescence (LIF) spectra of isobutoxy, 2-methyl-1-butoxy, and 3-methyl-1-butoxy in supersonic jet-cooled condition. Ground state unimolecular decomposition and isomerization as well as excited state relaxation dynamics of isobutoxy were discussed in combination with the theoretical calculations. Analysis of the experimental and theoretical results showed that methyl substitution on the β carbon of the alkoxy radicals changed the LIF spectra of alkoxy radicals significantly. The competition between the ground state reactions and the photoexcitation process depended strongly on the radical structure and hence affected the involvement of alkoxy radicals in the photochemical reactions in the upper troposphere. This study will help to understand the dynamic role of alkoxy radicals in the atmosphere.

Cyclohexoxy and its methyl substituted variants play an important role in atmospheric chemistry. Direct spectral observation of these radicals can provide information about their structures and serve as convenient diagnostics for their monitoring. In this work, we report the first time observation of the LIF spectra of 2-, 3-, and 4-methylcyclohexoxy radicals in supersonic jet-cooled conditions. All spectra are consistent with a single conformer, and thermodynamic analysis of the conformers suggests that the conformer has the diequatorial (e, e) chair structure. Vibrational frequency analysis was performed using CASSCF/6-31+G(d) method on the state of radicals and the vibronic bands were assigned. The origin band of the methyl substituted cyclohexoxy shifted to red with the decrease of the separation distance between the methyl group and the oxygen atom on the ring. Different spectral character of 2-methylcyclohexoxy radical suggested that the neighboring methyl group affected the behavior of the radical on the excited state.

Cyclohexoxy radical and its substitutes are intermediates of the combustion reaction in automobile engines, and hence play an important role in the atmospheric chemistry. Spectroscopic and conformational studies can provide convenient methods to monitor these species. In this work, we report the observation of the laser induced fluorescence (LIF) excitation spectrum of 1-methylcyclohexoxy, a tertiary ring alkoxy radical, in supersonic jet condition. The spectrum was assigned preliminarily to the chair-axial and chair-equatorial conformers of 1-methylcyclohexoxy. No C–O stretch progression was observed in 1-methylcyclohexoxy spectrum, which was different from t-butoxy. The short lifetime of excited state 1-methylcyclohexoxy and increased C–O bond length suggested a less stable excited state induced by the increased steric repulsion via methyl substitution on the alkoxy carbon. Dissociation rather than H transfer was suggested as the major nonradiative relaxation process, which competed with the fluorescence path.

Alkoxy radicals are important intermediates in the formation of tropospheric ozone. The spectroscopic identification and characterization of these species are important for understanding their chemistry in the atmosphere. In this work, we report the observation of the laser induced fluorescence (LIF) excitation spectrum of cycloheptoxy radical. The spectrum was assigned preliminary to the lowest energy twist-chair conformer (TC-i) of cycloheptoxy. The whole picture of the interconversions at ground state between different conformers of cycloheptoxy radicals was described by density functional theory calculations. The results revealed that despite the ring strain, the seven-membered ring alkoxy radical could exist in the supersonic jet-cooled condition. The decomposition and the low energy barrier pseudorotation between twist-chair conformers might be the reason of the much quieter spectrum of cycloheptoxy compared with the LIF spectrum of cyclohexoxy.

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 (NOx). 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.