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This theoretical study uses ab initio quantum mechanical methods to investigate the electronic properties of ground and excited state sodium nitrate. We calculated electronic properties of the crystalline material for bulk, clean, and defected surfaces. The results of these calculations are used to explain the photoexcitation/desorption mechanism and support the conclusions of an earlier experimental investigation of the laser desorption of NO from single-crystal sodium nitrate. The calculations indicate that the electronic structure of the bulk and cleavage surface are virtually identical (i.e., no shift in the resonant absorption profile is expected). This finding is consistent with the experimental results on the wavelength dependence of NO desorption yields for crystalline NaNO{sub 3}. However, changes in the absorption manifold are found to accompany the removal of external nitrate oxygens (producing surface nitrite groups). The presence of these chemical defects causes states to appear in the band gap producing a red shift in the absorption band. These calculations also indicate that the transition energies of the nitrate ion are unaffected by the presence of the surrounding ions. 34 refs., 8 figs., 2 tabs.

We have studied the laser desorption of NO from single crystal sodium nitrate following pulsed 213-nm excitation of the {pi}{sup *} {yields} {pi}{sub 2} absorption band localized on the nitrate anion. At low fluence, the NO photodesorption yield is found to be linear with desorption laser power indicating that single-photon absorption events lead to fragment ejection. The desorption yield is enhanced by roughly a factor of 1000 for resonant excitation (213 nm) over nonresonant excitation (266 nm) on a per-photon basis. We determine the relative vibrational, rotational, and translational energy distributions of the neutral NO photoproducts. Significant population in vibrational levels up to v{double_prime} = 4 is observed and translational distributions for the v{double_prime} = 0-3 levels are determined. A local excitation mechanism for NO desorption following resonant excitation is proposed. Under these experimental conditions the resonant desorption process (213 nm) is dominated by the photochemistry of the surface nitrate ions. A model for the absorption/dissociation mechanism is proposed that differs from that reported for gas phase ions in that it accounts for the stabilization of the ions due to the crystalline field. The role of exciton migration following resonant excitation is also discussed. 42 refs., 7 figs.

The photofragment ion imaging technique is used to measure the velocity distributions of atomic chlorine, methyl, and carbon monoxide fragments generated in the photodissociation of acetyl chloride at 236 nm. The fragments are selectively ionized by (2 + 1) multiphoton ionization and projected onto a two-dimensional position-sensitive detector to obtain speed and angular distributions. The Cl images display anisotropic angular distributions, characteristic of a prompt, impulsive dissociation of the C-Cl bond. A fraction of the CH[sub 3]CO, produced as a primary photoproduct, subsequently decomposes to form CH[sub 3] and CO. The CH[sub 3] and CO images are isotropic, suggesting that rotation of the acetyl radical intermediate occurs prior to the secondary dissociation. The internal state distribution of CO is probed using (2 + 1) multiphoton ionization via the B[sup 1][Sigma][sup +] state near 230 nm. The rotational state distribution of CO extends to J[double prime] = 30, while no vibrational excitation is observed. The transition state structure of the CH[sub 3]CO intermediate, leading to dissociation into CH[sub 3] and CO, is computed via ab initio quantum mechanical methods. 42 refs., 7 figs., 4 tabs.

Absolute rate coefficients for the reactions of CN with ethane, propane, and five of their deuterated isotopes are determined over the temperature range 294-736 K by using the laser photolysis/CW laser-induced-fluorescence technique. The measured rate coefficients for the reactions of CN with C{sub 2}H{sub 6} (k{sub 1}) and C{sub 2}D{sub 6} (k{sub 2}) are well described by the three-parameter modified Arrhenius expressions k{sub 1}(T) = (7.40 {times} 10{sup {minus}15})T{sup 1.29} exp(+512 cal mol{sup {minus}1}/RT) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} and k{sub 2}(T) = (8.32 {times} 10{sup {minus}16})T{sup 1.57} exp(+460 cal mol{sup {minus}1}/RT) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. The rate coefficient for the reaction of CN with the half-deuterated ethane compound, CH{sub 3}CD{sub 3} (k{sub 3}), is well described ty (1/2)(k{sub 1} + k{sub 2}). We measure rate coefficients for CN reactions with C{sub 3}H{sub 8} (k{sub 4}), C{sub 3}D{sub 8} (k{sub 5}), C{sub 3}H{sub 6}D{sub 2} (k{sub 6}), and C{sub 3}D{sub 6}H{sub 2} (k{sub 7}) and derive site-specific rate constants for abstraction of primary and secondary hydrogens. These rate coefficients, on a per hydrogen atom basis, are, in the units cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, k{sub H}{sup P}(T) = (3.58 {times} 10{sup {minus}15})T{sup 1.14} exp(+566 cal mol{supmore » {minus}1}/RT), k{sub D}{sup P}(T) = (2.63 {times} 10{sup {minus}16})T{sup 1.47} exp(+568 cal mol{sup {minus}1}/RT), k{sub H}{sup S}(T) = (3.30 {times} 10{sup {minus}13})T{sup 0.56} exp(+649 cal mol{sup {minus}1}/RT), and k{sub D}{sup S}(T) = (2.96 {times} 10{sup {minus}13})T{sup 0.52} exp(+656 cal mol{sup {minus}1}/RT). The k{sub 4} through k{sub 7} are well represented by the sum of the appropriate three-parameter expressions for H- and D-atom abstraction from primary and secondary sites.« less

The A tilde formed from X tilde transition in ammonia is investigated by direct ultraviolet absorption spectroscopy of samples cooled in supersonic jet expansions. Franck-Condon factors are reported here for this transition of NH/sub 3/ and ND/sub 3/: they are considerably different from those available from room-temperature data. The spectra are discussed in light of models available for the A state ammonia.

Absolute rate coefficients for the reactions of OH with CH{sub 3}OH (k{sub 1}) and CD{sub 3}OH (k{sub 2}) were measured over the temperature range 293-866 K by using the laser photolysis/laser-induced fluorescence technique. The kinetic data, in the units cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, are fitted to the three-parameter expressions k{sub 1}(T) = 5.89 {times} 10{sup {minus}20}T{sup 2.65} exp(+883 cal mol{sup {minus}1}/RT) and k{sub 2}(T) = 1.28 {times} 10{sup {minus}22}T{sup 3.48} exp(+1275 cal mol{sup {minus}1}/RT). The measured kinetic isotope effect, k{sub 1}/k{sub 2}, yields insight into the branching ratio for H-atom abstraction from the methyl versus the hydroxyl site in methanol.