A study of the UV—visible absorption spectra of Br2 and BrCl

Abstract A mathematical representation of the UV—visible absorption spectrum of Br 2 vapour, which is based on a four-band semi-logarithmic gaussian distribution function, was derived in an assessment of the literature spectra where tanhtanh( hc ×325.3213 cm −1 /2 kT and λ is the wavelength in vacuum (200⩽λ⩽650 nm). The UV—visible absorption spectrum of BrCl (200⩽λ⩽600 nm) and the equilibrium coefficient for the reaction (Br 2 ) g + (Cl 2 ) g ← K BrCl → 2(BrCl) g were obtained by analysis of the absorption spectra of gaseous mixtures of Cl 2 and Br 2 , which were investigated at 298 K with a spectral resolution of 0.2 nm. The absorption cross-sections of BrCl are in good agreement with those reported by other workers and can be adequately described by a three-band semi-logarithmic gaussian distribution function where tanhtanh( hc ×443.1 cm −1 /2 kT ) and λ is the wavelength in vaccum (200⩽λ⩽600 nm). In contrast with the spectrum of Br 2 vapour, no evidence was found for a fourth band in the spectrum of BrCl in the wavelength range studied. The value obtained for the equilibrium coefficient K BrCl (298 K)[BrCl] 2 /([Br 2 ][Cl 2 ]) = 10.1±1.1 is the largest reported so far. This yields a standard enthalpy for the formation of BrCl of Δ H BrCl °(298 K) = 14 307 J mol −1 .

[1]  S. Sander,et al.  Kinetics and product studies of the BrO + ClO reaction - Implications for Antarctic chemistry , 1988 .

[2]  J. Tellinghuisen.  Spontaneous predissociation in BrCl: A possible role for shape resonances in threshold predissociation , 1988 .

[3]  P. Stephens,et al.  Magnetic circular dichroism spectra of the halogen molecules, I2, Br2 and Cl2. Resolution of overlapping O+u (3II) and 1II bands , 1974 .

[4]  J. Wiesenfeld,et al.  Measurement of the A 3π1u←X 1Σ+g continuum absorptivity in Br2 , 1979 .

[5]  J. Crowley,et al.  2-Bromoethylperoxy and 2-bromo-1-methylpropylperoxy radicals: ultraviolet absorption spectra and self-reaction rate constants at 298 K , 1992 .

[6]  D. R. Hanson,et al.  The reaction probabilities of ClONO2 and N2O5 on polar stratospheric cloud materials , 1991 .

[7]  R. Stolarski,et al.  Nimbus 7 satellite measurements of the springtime Antarctic ozone  decrease , 1986, Nature.

[8]  S. B. Moore,et al.  Heterogeneous reactions on nitric acid trihydrate , 1990, Nature.

[9]  J. Tellinghuisen,et al.  The E → B transition in 81Br37Cl , 1988 .

[10]  R. A. Cox,et al.  Organic peroxy radicals: Kinetics, spectroscopy and tropospheric chemistry , 1992 .

[11]  L. Barrie,et al.  Photochemical bromine production implicated in Arctic boundary-layer ozone depletion , 1992, Nature.

[12]  K. Neumann,et al.  Die thermische Dissoziation des wasserfreien Natriumthiosulfats unterhalb 300°C , 1976 .

[13]  P. Stephens,et al.  The magnetic circular dichroism spectrum of the halogen molecules I2, Br2, Cl2. Resolution of overlapping continua , 1975 .

[14]  J. Burrows,et al.  Absorption cross-sections of NO2 in the UV and visible region (200 – 700 nm) at 298 K , 1987 .

[15]  R. F. Barrow,et al.  The B 3Π0u+-X 1Σg+ system of Br2: Rotational analysis, Franck-Condon factors, and long range potential in the B 3Π0u+ state , 1974 .

[16]  S. Solomon,et al.  On the depletion of Antarctic ozone , 1986, Nature.

[17]  S. Wofsy,et al.  Reductions of Antarctic ozone due to synergistic interactions of chlorine and bromine , 1986, Nature.

[18]  E. Wolff,et al.  Reactions on sulphuric acid aerosol and on polar stratospheric clouds in the Antarctic stratosphere , 1991 .

[19]  N. S. Bayliss,et al.  The Continuous Absorption Spectrum of Bromine: A New Interpretation , 1936 .

[20]  N. S. Bayliss,et al.  Effect of Foregin Gases on the Continuous Absorption Spectrum of Bromine , 1939, Nature.

[21]  R. M. Noyes,et al.  Ultraviolet spectra of single and double molecules of gaseous bromine , 1972 .

[22]  D. Seery,et al.  The Continuous Absorption Spectra of Chlorine, Bromine, Bromine Chloride, Iodine Chloride, and Iodine Bromide , 1964 .

[23]  D. D. Wagman,et al.  Thermodynamic properties of some gaseous halogen compounds , 1955 .

[24]  J. Farman,et al.  Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction , 1985, Nature.

[25]  B. Edĺen.  The Refractive Index of Air , 1966 .

[26]  M. Molina,et al.  Antarctic Stratospheric Chemistry of Chlorine Nitrate, Hydrogen Chloride, and Ice: Release of Active Chlorine , 1987, Science.

[27]  N. S. Bayliss,et al.  The absorption spectrum of bromine vapour in the region 3400 A. to 2200 A. , 1938 .

[28]  R. L. Roy,et al.  Diatom potential curves and transition moment functions from continuum absorption coefficients: Br2 , 1976 .

[29]  H. M. Crosswhite,et al.  The Iron-Neon Hollow-Cathode Spectrum. , 1975, Journal of research of the National Bureau of Standards. Section A, Physics and chemistry.

[30]  E. W. Pearson,et al.  Laboratory Studies of Sticking Coefficients and Heterogeneous Reactions Important in the Antarctic Stratosphere (Paper 7L6697) , 1988 .

[31]  S. Solomon.  Progress towards a quantitative understanding of Antarctic ozone depletion , 1990, Nature.

[32]  G. Ribaud.  Contribution à l'étude de l'absorption de la lumière par les gaz , 1919 .

[33]  M. Heaven,et al.  Theoretical treatment of the spontaneous predissociation of Br2, B 3Π(0u+) , 1982 .

[34]  P. Morse.  Diatomic Molecules According to the Wave Mechanics. II. Vibrational Levels , 1929 .

[35]  M. Prather.  More rapid polar ozone depletion through the reaction of HOCI with HCI on polar stratospheric clouds , 1992, Nature.

[36]  A. Rees.  Note on the interpretation of the visible absorption spectrum of bromine , 1947 .

[37]  D. Golden,et al.  Reaction of Chlorine Nitrate with Hydrogen Chloride and Water at Antarctic Stratospheric Temperatures , 1987, Science.

[38]  A. Jenouvrier,et al.  O2 Herzberg continuum absorption cross-sections in the wavelength region 196–205 nm of the Schumann Runge bands , 1990 .

[39]  F. Zaraga,et al.  Transition moment, radiative lifetime, and quantum yield for dissociation of the 3Π0+u state of 81Br2 , 1976 .

[40]  F. Bien,et al.  Intensity and collision half-width measurements using a laser source—II. Continuum and line absorption of Br2 at 6328 A , 1967 .

[41]  H. Johnston,et al.  Oxygen absorption cross sections in the herzberg continuum and between 206 and 327 K , 1984 .

[42]  D. R. Stull.  JANAF thermochemical tables , 1966 .

[43]  J. A. Coxon.  Rotational vibrational analysis of the B3Π (0+) - X1Σ+ band system of 79Br35Cl and 81Br35Cl , 1974 .

[44]  R. P. Crannage,et al.  Long wavelength vibronic band analysis of the B 3Π(0+)→X 1Σ+ transitions of 79Br35Cl and 81Br35Cl , 1989 .

[45]  J. Burrows,et al.  A study of the UV—visible absorption spectrum of molecular chlorine , 1993 .

[46]  D. W. G. Style,et al.  The Absorption of Light by Chlorine, Bromine and their Gaseous Mixtures , 1930 .

[47]  S. Wofsy,et al.  Chemistry of OClO in the Antarctic stratosphere: implications for bromine , 1988 .

[48]  M. Molina,et al.  The heterogeneous reaction of HOCl + HCl ? Cl2 + H2O on ice and nitric acid trihydrate: Reaction pro , 1992 .

[49]  J. D. Christian,et al.  The ultraviolet-visible absorption spectrum of bromine between room temperature and 440° , 1967 .

[50]  D. R. Hanson,et al.  Investigation of the reactive and nonreactive processes involving nitryl hypochlorite and hydrogen chloride on water and nitric acid doped ice , 1992 .

[51]  R. S. Mulliken.  Halogen Molecule Spectra. II. Interval Relations and Relative Intensities in the Long Wave-Length Spectra , 1940 .

[52]  S. B. Moore,et al.  Heterogeneous reactions of chlorine nitrate and hydrogen chloride on type I polar stratospheric clouds , 1991 .