OD Reaction Research Articles

Laser probing of nascent gaseous product species formed in chemical reactions on surfaces

A review of research conducted at the Naval Research Laboratory illustrates the unique advantages of using lasers to probe the newly formed gaseous products from chemical reactions on surfaces. Examples to be discussed are taken from the areas of catalytic reactions, silicon etching, and surface photochemistry. UHV experiments on the catalytic oxidation of H2, D2, and NH3 by 02 and of H2 by NO2 used the laser-induced fluorescence technique to measure the apparent desorption energies of OH radicals and the rotational energy accommodation of the desorbing OH, OD, and NO reaction products. The observed different degrees of "rotational cooling" in the different products are discussed. In multiphoton ionization mass spectrometry (MPI/MS) experiments, spectroscopies of three different MPI processes for the SiF2 radical were studied and two of these were applied to the study of silicon etching by XeF2, F2, and NF3. The only observed gaseous products were SiF4 and the SiF2 radical and their apparent production energies correlated with the ease of surface fluorine atom production. In the area of surface photochemistry, an excimer laser was used to photolyze iodobenzene, trimethylgallium, and trimethylindium adsorbed on a cold surface. The time-of-flight spectra of the fragments or reaction products were measured by using a mass spectrometer equipped with MPI or electron ionization (El).

Kinetics and mechanism of hydroxyl radical reaction with methyl hydroperoxide

The reaction of hydroxyl radical with methyl hydroperoxide, CH{sub 3}OOH, was investigated in the temperature range 203-423 K by pulsed photolytic generation of OH and detection by laser-induced fluorescence. The rate coefficient for the overall reaction, OH + CH{sub 3}OOH {yields} products (k{sub 1}) was measured by using {sup 18}OH and OD in place of OH. The rate coefficient for the CH{sub 3}O{sub 2} production channel OH + CH{sub 3}OOH {yields} CH{sub 3}O{sub 2} + H{sub 2}O (k{sub 1a}) was obtained by using OH. The channel that yields CH{sub 2}OOH, OH + CH{sub 3}OOH {yields} CH{sub 2}OOH + H{sub 2}O (k{sub 1b}), is not observed when monitoring OH since CH{sub 2}OOH rapidly falls apart to give back OH (and CH{sub 2}O) but is observed when studying the {sup 18}OH or OD reaction with CH{sub 3}OOH. By monitoring OH production in OD + CH{sub 3}OOH reaction at 249 K, the two-channel mechanism was confirmed, and the values for k{sub 1} and k{sub 1a} were also determined. Both reaction 1 and channel 1a show negative activation energies, with k{sub 1} = (2.93 {plus minus} 0.30) {times} 10{sup {minus}12} exp((190 {plus minus} 14)/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} (average of {sup 18}OHmore » and OD studies) and k{sub 1a} = (1.78 {plus minus} 0.25) {times} 10{sup {minus}12} exp((220 {plus minus} 21)/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, where the indicated error is 1 {sigma}, including estimated systematic errors and {sigma}{sub A} = A{sigma}{sub lnA}. The rate coefficient for the reaction of OD with CH{sub 3}OOD is at least a factor of 2 smaller than that for reaction 1a. The thermal decomposition lifetime for CH{sub 2}OOH to give OH + CH{sub 2}O is deduced to be shorter than 20 {mu}s at 205 K. The mechanism of reaction 1 and the implications of our kinetic and mechanistic results to Earth's atmospheric chemistry are discussed.« less

The reaction of OH and OD with nitromethane and OD with perdeuteronitromethane

Laser photolysis/laser-induced fluorescence (LIF) is employed to investigate the kinetics of the reactions, OH+CH 3NO 2, OD+CH 3NO 2, and OD+CD 3NO 2 over the temperature range 296–671 K. Photolysis of nitromethane at 266 nm generates OH or OD radicals. Rate constants are independent of pressure over the range 100–300 Torr. The following Arrhenius equations are calculated: k =(1.1±0.4)x10 −12 exp[−(2730±290 cal/mol)/ RT] cm 3 s −1 for OH, OD+CH 3NO 2 and k =(5.3±2.4)×10 −13 exp[−(2860±340 cal/mol)/ RT] cm 3 s −1 for OD+CD 3NO 2. A hydrogen atom abstraction mechanism is supported by evidence from isotopic studies, transition-state theory calculations, absence of pressure effects, known energetics, and measured activation energies. Transition-state theory (TST) calculations predict non-Arrhenius behavior as temperatures approach the combustion regime. The TST calculation is fit by the equation, k = 4.37 × 10 −20 T 2.4 exp(− 340/T) cm 3 s −1 over the temperature range 200–2000 K.

A comparison of rotational energy accommodation in catalytically produced OD and OH radicals desorbing from a smooth Pt(111) single crystal

Rotational energy distributions of OD and OH radical reaction products desorbing from a smooth Pt(111) single crystal surface have been measured under closely similar experimental conditions by using the laser-induced fluorescence technique in conjunction with an UHV apparatus. Over the temperature ranges studied, nearly full rotational energy accommodation was observed for OD with a rotational to surface temperature ratio, Tr/Ts =0.96±0.04, and a somewhat lower ratio of 0.86±0.05 was obtained for OH. For both OD and OH the spin–orbit temperatures were the same as the rotational temperatures and no preference for any lambda-doublet state was observed.

Reaction dynamics of O(1D2)+H2, HD, D2: OH, OD(X 2Πi) product internal energy distributions

Partial internal energy distributions of the hydroxyl reaction products of O(1D)+H2, HD, and D2 reactions are presented. Inverted rotational distributions, preferential population of the π+ lambda doubling sublevels, and statistical population of the spin sublevels are observed. A slight preferential formation of the OD vs OH reaction products observed is measured for the reaction of O(1D)+HD. Surprisal analysis of these results indicates both dynamical and kinematic constraints on the reaction dynamics. Comparison of these results with published model calculations suggest that an insertion mechanism to form a highly energetic collision complex dominates the reaction dynamics.

Optical detection of ESR spectra from short-lived radical-ion pairs in spurs under radiolysis

Principles of the method of optical detection of ESR spectra from radical-ion pairs in solutions are considered. Apparatus for detection of these spectra is described. Some examples of studying OD ESR spectra and reactions of radical-ion pairs arising in solutions under ionizing irradiation are discussed.

The pressure dependence of the rate constant for the reaction of OD with CO

The pressure dependence of the rate constant for the reaction of OD with CO

An infrared spectroscopic study of the promotion of the metal-catalyzed exchange of silica OH groups with gaseous deuterium

A study has been made of the metal-catalyzed exchange of silica OH groups of an indium-silica catalyst with deuterium gas at 25 °C. This catalytic reaction proceeds more slowly on ‘hydrogen-covered’ than on ‘bare’ indium, and does not proceed measurably on silica alone at this temperature. However, a considerable number of preadsorbed molecules have been found to promote this catalytic reaction; acetal-dehyde, chloral (1,1,1-trichloroacetaldehyde), and acetonitrile lead to an OH → OD reaction with a half life of less than 5 min. A few experiments indicate that chloral-promoted platinum-silica also leads to very rapid exchange.