Photodissociation of formaldoxime and its methylated homologues: Search for H sub 2 CN fluorescence

Journal Article · Thu Aug 10 00:00:00 EDT 1989 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100353a024· OSTI ID:7156969

Dagdigian, P J ^[1]; Anderson, W R; Sausa, R C; Miziolek, A W ^[2]

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1. Johns Hopkins Univ., Baltimore, MD (USA)
2. Ballistic Research Lab., MD (USA)

The photodissociation of formaldoxime (H{sub 2}CNOH), formaldazine (H{sub 2}CNNCH{sub 2}), and their methylated homologues at 193 and 248 nm has been studied with emphasis on oxime photolysis at 193 nm. The primary objective was to search for laser-induced fluorescence (LIF) of the R{sub 1}R{sub 2}CN radical (R{sub 1}, R{sub 2} = H or CH{sub 3}) which is expected to be produced as a primary product of the photolysis. No LIF was observed upon irradiation in the regions where the radicals are known to absorb, 280-295 nm. Assuming the density of R{sub 1}R{sub 2}CN equals that of OH produced by photolysis of the oximes at 193 nm, upper limits for the quantum yield of fluorescence of 0.01 are calculated for CH{sub 3}CHN and (CH{sub 3}){sub 2}CN and of 0.1 for H{sub 2}CN. The authors therefore conclude it is highly likely the upper states of these radicals probed in the 280-295-nm region are predissociative, which is consistent with results of previous absorption experiments. The LIF spectra of the OH fragments produced from photolysis of the oximes at 193 nm were also studied. The dependence of the OH fragment LIF intensity on excimer laser power indicates a one-photon dissociation process, as expected from energetic considerations. The nascent OH rotational distribution is much hotter than for a room temperature Boltzmann distribution; the ratio of densities for {nu} = 1 to {nu} = 0 vibrational levels is 0.02 {plus minus} 0.01. Only 2.5 kcal/mol of the excess energy appears as OH product internal energy, thus leaving about 80 kcal/mol to be divided between the R{sub 1}R{sub 2}CN fragment and translation. CN in its ground X{sup 2}{Sigma}{sup +} state was also detected via LIF in its B-X band system upon 193-nm photolysis o CH{sub 3}CHNOH. Results of a power dependence study were consistent with a single-photon process to yield this product, which is energetically possible if the products are CH{sub 4} + CN + OH.

• OSTI ID: 7156969
• Journal Information: Journal of Physical Chemistry; (USA), Vol. 93:16; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
FORMALDEHYDE
PHOTOCHEMISTRY
DATA ANALYSIS
DISSOCIATION
EXPERIMENTAL DATA
FLUORESCENCE
MEASURING INSTRUMENTS
MEASURING METHODS
PHOTOLYSIS
ALDEHYDES
CHEMICAL REACTIONS
CHEMISTRY
DATA
DECOMPOSITION
INFORMATION
LUMINESCENCE
NUMERICAL DATA
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
400000* - Chemistry
400500 - Photochemistry
400800 - Combustion
Pyrolysis
& High-Temperature Chemistry