Leon F. Phillips

Rate constant for quenching of CO2(010( by atomic oxygen

The rate of quenching of CO[sub 2](010) by O([sup 3]P) has been measured at room temperature by a temperature-jump method. The rate constant value obtained is in good agreement with a previous room-temperature measurement based on steady-state analysis of a hollow-cathode discharge in CO[sub 2]. The results of fitting the room-temperature result to trajectory calculations with a curve-crossing (Nikitin) energy-transfer mechanism lead to the conclusion that the quenching rate constant should increase only slowly with increasing temperature. 12 refs., 4 figs.

Kinetics of reactions of NH with NO and NO2

Abstract Ground-state NH radicals were generated by 248 nm KrF laser photolysis of N2H4 and their concentration monitored by laser-induced fluorescence at 336 nm, at total pressures near 1 Torr and temperatures between 269 and 377 K. He, Ar, N2 and N2O were used as carrier gases. Rate constants obtained at 300 K are (1.61 ± 0.14) × 10− for NH + NO2 and (5.78 ± 0.64) × 10−11 for NH + NO (units cm3 molecule−1s−1). For NH + NO the rate constant is independent of temperature over the range studied; for NH + NO2 there is a small negative temperature dependence. Within experimental error, results at 300 K are independent of the choice of carrier gas. The results are discussed in terms of a mechanism involving an intermediate HNNO or HNNO2 complex.

Enhanced photolysis in aerosols: evidence for important surface effects

While there is increasing evidence for unique chemical reactions at interfaces, there are fewer data on photochemistry at liquid-vapor junctions. This paper reports a comparison of the photolysis of molybdenum hexacarbonyl, Mo(CO)(6), in 1-decene either as liquid droplets or in bulk-liquid solutions. Mo(CO)(6) photolysis is faster by at least three orders of magnitude in the aerosols than in bulk-liquids. Two possible sources of this enhancement are considered: (1) increased light intensity due to either Morphology-Dependent Resonances (MDRs) in the spherical aerosol particles and/or to increased pathlengths for light inside the droplet due to refraction, which are termed physical effects in this paper; and (2) interface effects such as an incomplete solvent-cage at the gas-liquid boundary and/or enhanced interfacial concentrations of Mo(CO)(6), which are termed chemical effects. Quantitative calculations of the first possibility were carried out in which the light intensity distribution in the droplets averaged over 215-360 nm was obtained for 1-decene droplets. Calculations show that the average increase in light intensity over the entire droplet is 106%, with an average increase of 51% at the interface. These increases are much smaller than the observed increase in the apparent photolysis rate of droplets compared to the bulk. Thus, chemical effects, i.e., a decreased solvent-cage effect at the interface and/or enhancement in the surface concentration of Mo(CO)(6), are most likely responsible for the dramatic increase in the photolysis rate. Similar calculations were also carried out for broadband (290-600 nm) solar irradiation of water droplets, relevant to atmospheric conditions. These calculations show that, in agreement with previous calculations by Mayer and Madronich [B. Mayer and S. Madronich, Atmos. Chem. Phys., 2004, 4, 2241] MDRs produce only a moderate average intensity enhancement relative to the corresponding bulk-liquid slabs when averaged over a range of wavelengths characteristic of solar radiation at the Earths surface. However, as in the case of Mo(CO)(6) in 1-decene, chemical effects may play a role in enhanced photochemistry at the aerosol-air interface for airborne particles.

Rates of reaction of NH2 with N, NO AND NO2

Abstract The decay of NH 2 radicals, from 193 nm photolysis of NH 3 , was monitored by 597.7 nm laser-induced fluorescence. Room-temperature rate constants of (1.21 ± 0.14) × 10 −10 , (1.81 ± 0.12) × 10 −11 , and (2.11 ± 0.18) × 10 −11 cm 3 molecule −1 s −1 were obtained for the reactions of NH 2 with N, NO and NO 2 , respectively. The production of NH in the reaction of NH 2 with N was observed by laser-induced fluorescence at 336.1 nm.

Mass‐Spectrometric Studies of Atomic Reactions. V. The Reaction of Nitrogen Atoms with NO2

The reaction of N atoms with NO2 has been studied in a fast flow system, using a mass spectrometer to monitor the composition of the reaction mixture. The rate constant for removal of NO2 by N was found to be (1.85±0.22)×10−11 cm3 molecule−1·sec−1. By a combined mass‐spectrometric and photometric method the relative contributions of the different primary reactions have been determined as follows (errors shown are standard deviations): N+NO2→N2O+O (0.43±0.04),N+NO2→2NO (0.33±0.07),N+NO2→N2+O2 (0.10±0.12),N+NO2→N2+2O (0.13±0.11).

Fluorescence of aliphatic amines

Abstract Fluorescence of several tertiary aliphatic amines has been excited in the gas phase by absorption of 206.2 nm radiation, i.e. in the band corresponding to the A - X transition of NH3. No fluorescence was obtained from molecules having hydrogen or deuterium bonded directly to the nitrogen atom. The experiments support the view that quantum-mechanical tunnelling is the major factor governing the rates of predissociation of the excited states of NH3, ND3, and simple amines.

Rate of reaction of N with CN (υ = 0,1)

CN radicals were generated by 193 nm ArF laser flash photolysis of C2N2 in a fast-flow system, and their decay was monitored by dye-laser-induc

A priori rate constant for the reaction NH2+NO → N2+H2O

Abstract Capture rates for a dipole-dipole+Morse potential, from approximate semiclassical trajectory calculations, have been combined with RRKM rates for passing through entropy bottlenecks on the potential surface for NH 2 + NO → N 2 + H 2 O. The resulting overall rate constants are in good agreement with experiment. The effective lifetime of the NH 2 NO collision complex is found to be of the order of 10 −11 s at room temperature, which accounts for the observed lack of pressure dependence of the rate constant. Calculated rate constants increase markedly at low temperatures, though not as rapidly as some of the experimental data would indicate.

Complexes of HNO3 and NO3− with NO2 and N2O4, and their potential role in atmospheric HONO formation

Calculations were performed to determine the structures, energetics, and spectroscopy of the atmospherically relevant complexes (HNO(3)).(NO(2)), (HNO(3)).(N(2)O(4)), (NO(3)(-)).(NO(2)), and (NO(3)(-)).(N(2)O(4)). The binding energies indicate that three of the four complexes are quite stable, with the most stable (NO(3)(-)).(N(2)O(4)) possessing binding energy of almost -14 kcal mol(-1). Vibrational frequencies were calculated for use in detecting the complexes by infrared and Raman spectroscopy. An ATR-FTIR experiment showed features at 1632 and 1602 cm(-1) that are attributed to NO(2) complexed to NO(3)(-) and HNO(3), respectively. The electronic states of (HNO(3)).(N(2)O(4)) and (NO(3)(-)).(N(2)O(4)) were investigated using an excited state method and it was determined that both complexes possess one low-lying excited state that is accessible through absorption of visible radiation. Evidence for the existence of (NO(3)(-)).(N(2)O(4)) was obtained from UV/vis absorption spectra of N(2)O(4) in concentrated HNO(3), which show a band at 320 nm that is blue shifted by 20 nm relative to what is observed for N(2)O(4) dissolved in organic solvents. Finally, hydrogen transfer reactions within the (HNO(3)).(NO(2)) and (HNO(3)).(N(2)O(4)) complexes leading to the formation of HONO, were investigated. In both systems the calculated potential profiles rule out a thermal mechanism, but indicate the reaction could take place following the absorption of visible radiation. We propose that these complexes are potentially important in the thermal and photochemical production of HONO observed in previous laboratory and field studies.

Onsager heat of transport at the aniline liquid–vapour interface

Abstract The heat of transport for passage of matter through a gas–liquid interface has been determined for the aniline liquid–vapour system, by measuring stationary-state pressure differences produced by known temperature differences over a distance of 2 mm on the vapour side of the interface. For the range of pressures used, 2 mm is between 6 and 34 mean free paths. Coupling of the heat and matter fluxes is significant over the whole of this range. At the higher pressures the heat of transport is more than 20% of the heat of condensation; at the lower pressures it is more than 50%.