Scott L. Nickolaisen

California State University Los Angeles

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Stanley P. Sander

Berlin Institute of Health at Charité - Universitätsmedizin Berlin

Randall R. Friedl

Jet Propulsion Laboratory

Joseph S. Francisco

University of Pennsylvania

Charles E. Miller

Jet Propulsion Laboratory

William J. Bloss

University of Birmingham

R. J. Salawitch

University of Maryland, College Park

Lisa K. Blakeley

Purdue University West Lafayette

Ian H. Williams

University of Bath

Ruifeng Liu

China Earthquake Administration

Michael R. Hand

University of Bath

Cooperative Institutions

Jet Propulsion Laboratory

Purdue University West Lafayette

California Institute of Technology

East Tennessee State University

California State University Los Angeles

Max Planck Institute for Chemistry

NSF National Center for Atmospheric Research

Cooperative Institute for Research in Environmental Sciences

University of Bath

University of Colorado Boulder

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The OBrO C(2A2)←X(2B1) absorption spectrum

The Journal of Chemical Physics (1997)

Charles E. Miller Scott L. Nickolaisen Joseph S. Francisco Stanley P. Sander

The highly structured visible absorption spectrum of the bromine dioxide radical, OBrO, has been observed in the 15 500–26 000 cm−1 region. The spectrum is dominated by a long progression in the Br–O symmetric stretching motion (ν1′) and a series of short progressions built on the bending mode (ν2′); there are no features associated with the excitation of the antisymmetric stretching mode (ν3′). The spectrum also contains numerous transitions originating from the (0,1,0) and (1,0,0) vibrational levels of the electronic ground state, X(2B1). A simultaneous fit to all of the observed vibronic features yielded the frequencies ν1″=799.4 cm−1, ν2″=317.5 cm−1, ω1′=641.5 cm−1, ω2′=210.7 cm−1, and a band origin T0=15 863 cm−1. Franck–Condon simulations combined with ab initio calculations of the four lowest OBrO doublet electronic states identify the spectrum as arising from the C(2A2)←X(2B1) electronic transition.

Antisymmetric relation

Molecular electronic transition

10.1063/1.474606

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Citations (38)

ClO + ClO → Products: A Case Study in Halogen Monoxide Disproportionation and Recombination Reactions

Springer eBooks (1993)

Stanley P. Sander Scott L. Nickolaisen Randall R. Friedl

Monoxide

10.1007/978-3-642-78211-4_24

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Kinetics of the ClO Self-Reaction and 210 nm Absorption Cross Section of the ClO Dimer

The Journal of Physical Chemistry A (2001)

William J. Bloss Scott L. Nickolaisen R. J. Salawitch Randall R. Friedl Stanley P. Sander

The kinetics of the dimerization of ClO radicals, ClO + ClO + M → Cl2O2 + M (1a), and the 210 nm absorption cross sections of the ClO dimer have been studied using the technique of flash photolysis with UV absorption spectroscopy, over the temperature range 183−245 K and pressure range 25−700 Torr. ClO radicals were generated following the photolysis of Cl2/Cl2O/N2 mixtures and were quantified via their differential absorption between the peak of the (12,0) band of the (Ã ← X̃) transition at 275.2 nm and the adjacent minimum to higher wavelengths, while Cl2O2 formation was simultaneously monitored at 210 nm. ClO differential absorption cross sections were measured under identical conditions to the kinetic experiments by four separate calibration schemes. The rate coefficient measured at the lower temperatures studied (T < 200 K) was found to be up to 40% faster than extrapolation of previous results would suggest, with the limiting low- and high-pressure rate coefficients for reaction 1 in nitrogen determined to be k0 = (1.59 ± 0.60) × 10-32 × (T/300)-4.50±0.98 molecules-2 cm6 s-1 and k∞ = (1.36 ± 0.22) × 10-12 × (T/300)-3.09±0.40 molecules-1 cm3 s-1 respectively, obtained with Fc = 0.6. The corresponding value for k0 in air is k0(atm) = (1.49 ± 0.56) × 10-32 × (T/300)-4.50±0.98 molecules-2 cm6 s-1. The 210 nm absorption cross section of Cl2O2 was measured following time-resolved monitoring of its formation via ClO radical association, and a mean value of (2.94 ± 0.86) × 10-18 molecule-1 cm2 obtained, temperature independent (to within ± 15%) between 183 and 245 K. Errors are combined systematic uncertainties and 2 standard deviations statistical variation.

Flash photolysis

Absorption cross section

10.1021/jp012429y

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Pressure dependence and metastable state formation in the photolysis of dichlorine monoxide (Cl2O)

The Journal of Chemical Physics (1996)

Scott L. Nickolaisen Charles E. Miller Stanley P. Sander Michael R. Hand Ian H. Williams

The photodissociation of dichlorine monoxide (Cl2O) was studied using broadband flash photolysis to investigate the influence of variations in the photolysis wavelength domain, bath gas pressure and bath gas identity on the yield and temporal dependence of the ClO product. ClO yields were independent of bath gas pressure when the photolysis spectral band extended to 200 nm (quartz cutoff) but for photolysis restricted to wavelengths longer than about 250 nm, ClO yields decreased with increasing bath gas pressure and there was a pressure-dependent delay in the formation of ClO. Under these conditions, a weak, highly structured absorption spectrum was observed in the range 16 600–26 000 cm−1 with a lifetime on the order of 500 ms. A portion of the spectrum could be analyzed (22 000–26 000 cm−1) which showed progressions having differences of 283, 443, and 505 cm−1. Ab initio calculations were performed to evaluate vertical excitation energies and oscillator strengths from the lowest-energy singlet (X 1A1) or triplet (1 3B1) states to various excited states. The calculations indicated that the 2 3A2←1 3B1 transition has an unusually large oscillator strength. The transition energy, 3.05 eV, is consistent with the observed metastable spectrum. The observed pressure dependence of ClO formation could be modeled using a mechanism which assumed that Cl2O excitation at wavelengths longer than about 300 nm leads to rapid intersystem crossing to two metastable states in the triplet manifold. These states undergo competitive dissociation to ClO+Cl and collisional relaxation to the ground state. The dynamics of Cl2O may serve as a model for other molecules of importance in the earth’s lower stratosphere such as ClONO2 where filtering of the solar spectrum by ozone restricts photolysis to the weak tail of the absorption continuum.

Intersystem crossing

Metastability

Oscillator strength

Flash photolysis

10.1063/1.471109

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Pressure-Dependent Yields and Product Branching Ratios in the Broadband Photolysis of Chlorine Nitrate

The Journal of Physical Chemistry (1996)

Scott L. Nickolaisen Stanley P. Sander Randall R. Friedl

The photolysis of chlorine nitrate was studied using broadband flash photolysis coupled with long-path ultraviolet−visible absorption spectroscopy. Branching ratios for the Cl + NO3 and ClO + NO2 product channels were determined from time-dependent measurements of ClO and NO3 concentrations. Yields of the ClO and NO3 products displayed a dependence on the bath gas density and the spectral distribution of the photolysis pulse. Product yields decreased with increasing bath gas density regardless of the spectral distribution of the photolysis pulse; however, the decrease in product yield was much more pronounced when photolysis was limited to longer wavelengths. For photolysis in a quartz cell (λ > 200 nm) the yield decreased by a factor of 2 over the pressure 10−100 Torr. In a Pyrex cell (λ > 300 nm), the yield decreased by a factor of 50 over the same pressure range. When photolysis was limited to λ > 350 nm, the yield decreased by a factor of 250. Branching ratios for the photolysis channels [ClONO2 + hν → ClO + NO2 (1a) and ClONO2 + hν → Cl + NO3 (1b)] were determined from the relative ClO and NO3 product yields at various pressures. Although the absolute product yield displayed a pressure dependence, the branching between the two channels was independent of pressure. The relative branching ratios (assuming negligible contributions from other channels) are 0.61 ± 0.20 for channel 1a and 0.39 ± 0.20 for channel 1b for photolysis with λ > 200 nm and 0.44 ± 0.08 for channel 1a and 0.56 ± 0.08 for channel 1b for photolysis with λ > 300 nm. The implications of these results for the chemistry of the lower stratosphere are discussed.

Flash photolysis

Ultraviolet

10.1021/jp953612s

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Temperature Dependence of the HO₂+ ClO Reaction. 1. Reaction Kinetics by Pulsed Photolysis-Ultraviolet Absorption and ab Initio Studies of the Potential Surface

The Journal of Physical Chemistry A (1999)

Scott L. Nickolaisen Coleen M. Roehl Lisa K. Blakeley Randall R. Friedl Joseph S. Francisco

The kinetics of the HO2 + ClO reaction was studied using the flash photolysis/ultraviolet absorption technique over the temperature range 203−364 K and pressure range 50−700 Torr of N2. In contrast to previous work, the temperature dependence displayed linear Arrhenius behavior over the entire temperature range with the rate constant being described by the expression k(T) = 2.84 × 10-12 exp{(312 ± 60)/T} cm3 molecule-1 s-1. Ab initio calculations of intermediates and transition states have been carried out on the singlet and triplet potential energy surfaces. These calculations show that the reaction proceeds mainly through the ClO−HO2 complex on the triplet surface; however, collisionally stabilized HOOOCl formed on the singlet surface will possess an appreciable lifetime due to large barriers toward decomposition to HCl and HOCl. Termolecular rate calculations using ab initio parameters lead to a strong collision rate constant of ∼5 × 10-32 cm6 molecule-2 s-1 for HOOOCl formation. This intermediate may be important under both laboratory and atmospheric conditions.

Flash photolysis

Atmospheric temperature range

Potential energy surface

10.1021/jp992753h

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Citations (34)