Infrared Absorption Cross Sections Research Articles

Photolysis Study of Perfluoro-2-methyl-3-pentanone under Natural Sunlight Conditions

The UV-vis and infrared absorption cross sections of perfluoro-2-methyl-3-pentanone (CF3CF2C(O)CF(CF3)2, 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-penta none), has been obtained, and a photolysis study was carried out under natural sunlight conditions in the European simulation chamber, Valencia, Spain (EUPHORE). The photolysis loss rate, J(photol), equaled (6.4 +/- 0.3) x 10(-6) s(-1) in the period of 10-14 GMT, July 14, 2003 in Valencia (0.5 W, 39.5 N) and corresponded to an effective quantum yield of photolysis of 0.043 +/- 0.011 over the wavelength range of 290-400 nm; the error limits correspond to 2sigma from the statistical analyses. The atmospheric lifetime of CF3CF2C(O)CF(CF3)2 is estimated to be around 1 week, and the global warming potential of the compound is negligible.

Rate coefficients for the OH + CFH2CH2OH reaction between 238 and 355 K

The rate coefficient for the reaction OH + CFH2CH2OH --> products (k1) between 238 and 355 K was measured using the pulsed laser photolysis-laser induced fluorescence (PLP-LIF) technique to be (5.15 +/- 0.88)x 10(-12) exp[-(330 +/- 45)/T] cm3 molecule(-1) s(-1); k1(298 K)= 1.70 x 10(-12) cm3 molecule(-1) s(-1). The quoted uncertainties are 2sigma(95% confidence level) and include estimated systematic errors. The present results are discussed in relation to the measured rate coefficients for the reaction of OH with other fluorinated alcohols and those calculated using recently reported structure additivity relationships for fluorinated compounds (K. Tokuhashi, H. Nagai, A. Takahashi, M. Kaise, S. Kondo, A. Sekiya, M. Takahashi, Y. Gotoh and A. Suga, J. Phys. Chem. A, 1999, 103, 2664-2672, ). Infrared absorption cross sections for CFH2CH2OH are reported and they are used to calculate the global warming potentials (GWP) for CFH2CH2OH of approximately 8, approximately 2, and approximately 1, respectively, for the 20, 100 and 500 year horizons. A brief discussion of the atmospheric degradation of CFH2CH2OH is provided. It is concluded that CFH2CH2OH is an acceptable substitute for CFCs in terms of its impact on Earth's climate and the composition of the atmosphere. The room temperature rate coefficient for the reaction OH + CFH2CH2OH --> products (k10) was measured to be 3.26 x 10(-12) cm3 molecule(-1) s(-1), in good agreement with recent measurements from this laboratory.

Infrared photodissociation of (NO)n+·X cluster ions (n ≤ 5)

Measurements of the infrared photodissociation pathways and spectra of size-selected (NO)n +X complexes, for n in the range 2-5, have been carried out using a line-tuneable CO laser (photon energy 1600-1800 cm(-1)). X is one of Ar, Kr, Xe, O2, CO2, CH3Cl, CF4 or SF6. Two photoinduced fragmentation pathways have been monitored as a function of radiation wavelength: the loss of NO and the loss of X. The photofragmentation patterns and branching ratios are influenced by two factors: (i) the value of n; and to a lesser degree, (ii) the nature of the atom/molecule, X. A limited number of IR spectra have been recorded for the dimer, (NO)2+, in association with the rare gas atoms and CF4; for the remaining examples, the trimer, (NO)3+, appears to act as a stable core with a comparatively large infrared absorption cross-section at ca. 1720 cm(-1).

Atmospheric Chemistry of Hydrofluoroethers: Reaction of a Series of Hydrofluoroethers with OH Radicals and Cl Atoms, Atmospheric Lifetimes, and Global Warming Potentials

The kinetics of the OH radical and Cl atom reactions with nine fluorinated ethers have been studied by the relative rate method at 298 K and 1013 hPa using gas chromatography-mass spectroscopy (GC-MS) detection: k(OH + CH3CH2OCF3) = (1.55 +/- 0.25) x 10(-13), k(OH + CF3CH2OCH3) = (5.7 +/- 0.8) x 10(-13),k(OH + CF3CH2OCHF2) = (9.1 +/- 1.1) x 10(-15), k(OH + CF3CHFOCHF2) = (6.5 +/- 0.8) x 10(-15), k(OH + CHF2CHFOCF3) = (6.8 +/- 1.1) x 10(-15), k(OH + CF3CHFOCF3) < 1 x 10(-15), k(OH + CF3CHFCF2OCHF2) = (1.69 +/- 0.26) x 10(-14), k(OH + CF3CHFCF2OCH2CH3) = (1.47 +/- 0.13) x 10(-13), k(OH + CF3CF2CF2OCHFCF3) < 1 x 10(-15), k(Cl + CH3CH2OCF3) = (2.2 +/- 0.8) x 10(-12), k(Cl + CF3CH2OCH3) = (1.8 +/- 0.9) x 10(-11), k(Cl + CF3CH2OCHF2) = (1.5 +/- 0.4) x 10(-14), k(Cl + CF3CHFOCHF2) = (1.1 +/- 1.9) x 10(-15), k(Cl + CHF2CHFOCF3) = (1.2 +/- 2.0) x 10(-15), k(Cl + CF3CHFOCF3) < 3 x 10(-15), k(Cl + CF3CHFCF2OCHF2) < 6 x 10(-16), k(Cl + CF3CHFCF2OCH2CH3) = (3.1 +/- 1.1) x 10(-12), and k(Cl + CF3CF2CF2OCHFCF3) < 3 x 10(-15) cm3 molecule(-1) s(-1). The error limits include three standard deviations (3 sigma) from the statistical data analyses, as well as the errors in the rate coefficients of the reference compounds that are used. Infrared absorption cross sections and estimates of the trophospheric lifetimes and the global warming potentials of the fluorinated ethers are presented. The atmospheric degradation of the compounds is discussed.

Study of the OH and Cl-Initiated Oxidation, IR Absorption Cross-Section, Radiative Forcing, and Global Warming Potential of Four C4-Hydrofluoroethers

Infrared absorption cross-sections and OH and Cl reaction rate coefficients for four C4-hydrofluoroethers (CF3)2CHOCH3, CF3CH2OCH2CF3, CF3CF2CH2OCH3, and CHF2CF2CH2OCH3 are reported. Relative rate measurements at 298 K and 1013 hPa of OH and Cl reaction rate coefficients give k(OH+(CF3)2CHOCH3) = (1.27+/-0.13) x 10(-13), k(OH+CF3CH2OCH2CF3) = (1.51+/-0.24) x 10(-13), k(OH+CF3CF2CH2OCH3) = (6.42+/-0.33) x 10(-13), k(OH+CHF2CF2CH2OCH3) = (8.7 +/-0.5) x 10(-13), k(Cl+(CF3)2CHOCH3) = (8.4+/-1.3) x 10(-12), k(Cl+CF3CH2OCH2CF3) = (6.5+/-1.7) x 10(-13), k(Cl+CF3CF2CH2OCH3) = (4.0+/-0.8) x 10(-11), and k(Cl+CHF2CF2CH2OCH3) = (2.65+/-0.17) x 10(-11) cm3 molecule(-1) s(-1). The primary products of the OH and Cl reactions with the fluorinated ethers have been identified as esters, and OH and Cl reaction rate coefficients for one of these, CF3CH2OCHO, are reported: k(OH+CF3CH2OCHO) = (7.7+/-0.9) x 10(-14) and kCl+CF3CH2OCHO) = (6.3+/-1.9) x 10(-14) cm3 molecule(-1) s(-1) The rate coefficient for the Cl-atom reaction with CHF2CH2F is derived as k(Cl+CHF2CH2F) = (3.0+/-0.9) x 10(-14) cm3 molecule(-1) s(-1) at 298 K. The error limits include 3sigma from the statistical data analyses as well as the errors in the rate coefficients of the reference compounds employed. The tropospheric lifetimes of the hydrofluoroethers are estimated to be short tauOH((CF3)2CHOCH3) approximately 100 days, tauOH(CF3CH2OCH2CF3) approximately 80 days, tauOH(CF3CF2CH2OCH3) approximately 20 days, and tauOH(CHF2CF2CH2OCH3) approximately 14 days, and their global warming potentials are small compared to CFC-11.

Photodissociation of Vibrationally Excited Pernitric Acid: HO2NO2 (2ν1) + 390 nm

Pernitric acid (HO2NO2) molecule vibrationally excited in the vicinity of its first OH stretching overtone (2ν1) is dissociated via electronic excitation using 390-nm light. The nascent energy distribution of the resulting OH fragments is probed by using laser-induced fluorescence at sub-Doppler resolution. We find that for the minor OH + NO3 channel, 55% of the ∼19 600 cm-1of available energy goes into relative translation of the two fragments and 45% into internal excitation. In addition, electronically excited NO2 associated with the dominant HO2 + NO2 channel is also observed. The visible fluorescence from the excited NO2 fragments is sufficiently intense to allow vibrational action spectra of HO2NO2 to be recorded with good signal-to-noise. As vibrational states in the vicinity of the 2ν1 level can also undergo unimolecular dissociation on the ground electronic surface, comparing relative integrated intensities of spectral features appearing in the vibrational state selected action spectra with their known total infrared absorption cross sections provides a means for estimating unimolecular dissociation quantum yields from these levels under collision-free conditions. The present results indicate that at 298 K the unimolecular dissociation quantum yield for the HO2NO2 (2ν1) state is ∼30 ± 5%. Evidence is also presented for the generation of HOONO impurity in the standard synthesis route for HO2NO2.

Thermal infrared absorption cross-sections of CCl 4 needed for atmospheric remote sensing

Highly accurate spectral absorption cross-sections k ν ( cm 2 molecule −1 ) were measured in the 12.7 μm band of CCl 4 at temperatures between 208 and 296 K and pressures between 10 and 1013 mb with a high-resolution Fourier-transform spectrometer. Our data were obtained at pressures p and temperatures T that characterize the atmospheric layers in the commonly adapted models of the atmosphere. The selected ( p, T) combinations also represent tangent heights in solar-occultation-type remote sensing observations and actual conditions recorded by balloon-borne instruments in the Arctic. The combined absolute intensity (or integrated cross-section) of the bands contributing to the absorption around 12.7 μm is 6.295±0.102×10 −17 cm molecule −1 .

The infrared absorption cross-section and refractive-index data in HITRAN

The cross-sections and indices of refraction on the HIgh-resolution TRANsmission (HITRAN) database are summarized. HITRAN contains a tabulation of cross-sections of atmospheric chemical reservoir and source species, chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons, and indices of refraction of liquid and solid compounds. The temperature and pressure dependences of the cross-sections and the temperature dependence of the indices of refraction are illustrated. Data uncertainties and applications are discussed, and some future needs of the remote-sensing community are identified.

Thermal infrared absorption cross-sections of CF 4 for atmospheric applications

Spectral absorption cross-sections, k ν ( cm 2 molecule −1 ), have been measured in the 7.8 μm band of CF 4 at temperatures between 180 and 296 K and pressures between 10 and 1013 mb (hPa) with a high-resolution Fourier-transform spectrometer. Our data were obtained at pressures and temperatures that parameterize several of the commonly adapted model atmospheres, represent tangent heights in solar-occultation type remote-sensing observations of the atmosphere, and the conditions recorded in atmospheric observations at polar latitudes. The combined absolute intensity of all of the bands contributing to the absorption around 7.8 μm is (1.926±0.012)×10 −16 cm molecule −1 . The spectral absorption cross-section data have been incorporated into the two established and widely used spectroscopic databases.

Measurements of the infrared absorption cross-sections of haloalkanes and their use in a simplified calculational approach for estimating direct global warming potentials

The infrared absorption cross-sections and integrated band intensities (IBIs) for 21 haloalkanes: CFCl 3, CF 2Cl 2, CF 2Br 2, CH 2F 2, CHF 2Cl, CHF 2Br, CF 3Br, CHCl 2–CF 2Cl, CHFCl–CFCl 2, CHCl 2–CF 3, CHClBr–CF 3, CHFCl–CF 2Cl, CHFBr–CF 3, CHF 2–CF 3, CH 2Br–CF 3, CH 2F–CFCl 2, CH 2F–CF 3, CH 3–CCl 3, CH 3–CFCl 2, CH 3–CF 2–CF 3, and CHF 2–CH 2–CF 3 were measured over the wavenumber range 400–1600 cm −1 at T=295 K. The effect of air pressure on measured spectra was also investigated. These results are used to demonstrate a simple calculational approach for estimating the direct global warming potentials (GWPs) of such chemicals. The results obtained are compared with those derived from more comprehensive atmospheric modeling calculations appearing in the literature.

Detection and Identification of Donors in Hydride-Vapor-Phase Epitaxial GaN Layers

Low temperature photoluminescence experiments carried out on HVPE GaN samples produced in two different reactors are consistent with a low background level of donors and an extremely low concentration of compensating shallow acceptors. Infrared absorption experiments on these samples indicated that different shallow donors are incorporated at different rates in each reactor. High sensitivity SIMS was employed to measure the concentration of background impurities of a number of samples produced in both reactors. The comparison between the infrared absorption cross-sections with the SIMS results allows the identification of Si, the shallower, and O as the two dominant residual donors in these examples of HVPE GaN.

Detection and Identification of Donors in Hydride-Vapor-Phase Epitaxial GaN Layers

Low temperature photoluminescence experiments carried out on HVPE GaN samples produced in two different reactors are consistent with a low background level of donors and an extremely low concentration of compensating shallow acceptors. Infrared absorption experiments on these samples indicated that different shallow donors are incorporated at different rates in each reactor. High sensitivity SIMS was employed to measure the concentration of background impurities of a number of samples produced in both reactors. The comparison between the infrared absorption cross-sections with the SIMS results allows the identification of Si, the shallower, and O as the two dominant residual donors in these examples of HVPE GaN.

Updated radiative forcing estimates of 65 halocarbons and nonmethane hydrocarbons

The direct radiative forcing of 65 chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, hydrofluoroethers, halons, iodoalkanes, chloroalkanes, bromoalkanes, perfluorocarbons and nonmethane hydrocarbons has been evaluated using a consistent set of infrared absorption cross sections. For the radiative transfer models, both line‐by‐line and random band model approaches were employed for each gas. The line‐by‐line model was first validated against measurements taken by the Airborne Research Interferometer Evaluation System (ARIES) of the U.K. Meteorological Office; the computed spectrally integrated radiance of agreed to within 2% with experimental measurements. Three model atmospheres, derived from a three‐dimensional climatology, were used in the radiative forcing calculations to more accurately represent hemispheric differences in water vapor, ozone concentrations, and cloud cover. Instantaneous, clear‐sky radiative forcing values calculated by the line‐by‐line and band models were in close agreement. The band model values were subsequently modified to ensure exact agreement with the line‐by‐line model values. Calibrated band model radiative forcing values, for atmospheric profiles with clouds and using stratospheric adjustment, are reported and compared with previous literature values. Fourteen of the 65 molecules have forcings that differ by more than 15% from those in the World Meteorological Organization [1999] compilation. Eleven of the molecules have not been reported previously. The 65‐molecule data set reported here is the most comprehensive and consistent database yet available to evaluate the relative impact of halocarbons and hydrocarbons on climate change.

Infrared Absorption Cross-Section Measurements for Nitrous Acid (HONO) at Room Temperature

Infrared Absorption Cross-Section Measurements for Nitrous Acid (HONO) at Room Temperature

A potent greenhouse gas identified in the atmosphere: SF(5)CF(3)

We detected a compound previously unreported in the atmosphere, trifluoromethyl sulfur pentafluoride (SF(5)CF(3)). Measurements of its infrared absorption cross section show SF(5)CF(3) to have a radiative forcing of 0.57 watt per square meter per parts per billion. This is the largest radiative forcing, on a per molecule basis, of any gas found in the atmosphere to date. Antarctic firn measurements show it to have grown from near zero in the late 1960s to about 0.12 part per trillion in 1999. It is presently growing by about 0.008 part per trillion per year, or 6% per year. Stratospheric profiles of SF(5)CF(3) suggest that it is long-lived in the atmosphere (on the order of 1000 years).

Infrared absorption cross-sections and integrated absorption intensities of chloroform and fluoroform vapour

Infrared absorption cross-sections and integrated absorption intensities of chloroform (CHCl 3) and fluoroform (CHF 3) have been determined from laboratory measurements over a range of temperatures and air-broadened pressures by Fourier transform spectroscopy. Intercomparisons between these measurements and previous work have been made where possible.

Infrared absorption cross-sections and integrated absorption intensities of HFC-125 and HFC-143a

Infrared absorption cross-section and integrated absorption intensities of HFC-125 (pentafluoroethane) and HFC-143a (1,1,1-trifluoroethane) vapour have been calculated from their infrared spectra in the region 500–1400 and 700–1500 cm −1 for HCF-125 and HCF-143a, respectively. Spectra have been recorded by means of a Fourier transform spectrometer at a maximum resolution of 0.03 cm −1 at six temperatures in the range 203–293 K on the pure vapour and air mixtures at total pressures of 50, 200 and 800 hPa. A comparison between results obtained in this work and all the data reported previously in the literature has been reported.

Infrared absorption cross-sections and integrated absorption intensities for difluoromethane (HFC-32) and 1,1,1,2-tetrafluoroethane (HFC-134a) in the 650–50 cm −1 region

High-resolution (0.03 cm −1) infrared absorption cross sections and integrated absorption intensities for difluoromethane (HFC-32) and 1,1,1,2-tetrafluoroethane (HFC-134a) are reported for the 50–650 cm −1 spectral region. The data presented are for the pure vapour and for several mixtures with dry air, at a series of temperatures between ca. 200 K and room temperature. The absorption cross sections were calculated with and without correction for backward or sample emission, and it is shown that this correction can be important. The data are supported by ab initio calculations at a relatively high level of theory. The effect of buffer gas pressure and temperature on the integrated cross sections is discussed.

Infrared absorption cross-sections and integrated absorption intensities of perfluoroethane and cis-perfluorocyclobutane

Absorption cross-sections and integrated absorption intensities for the principal infrared bands of perflouroethane (C 2F 6) and cis-perfluorocyclobutane (c-C 4F 8) vapours have been derived from quantitative laboratory measurements of their spectra. Fourier transform spectroscopy using a resolution of 0.03 cm −1 over the spectral range 500–1900 cm −1 was employed. Measurements on pure vapour, and vapour/air mixtures were made, at sample temperatures between 203 and 293 K. Comparisons between these measurements and previously reported values have been made.

An intercomparison of laboratory measurements of absorption cross-sections and integrated absorption intensities for HCFC-22

An intercomparison of measurements of infra-red absorption cross-sections and integrated absorption intensities in HCFC-22 has been carried out. Independent measurements were made by five spectroscopy groups so that their experimental methods and data reduction techniques could be critically examined. The initial results showed a spread in reported values for integrated absorption intensity over the mid infra-red spectral region that were larger than the reported uncertainties. Re-examination of experimental and data reduction methods resulted in consistency of results within the reported errors. It was found that particular attention had to be paid to controlling and characterising errors associated with the non-linear response of MCT detectors and pre-amplifiers, adsorption of the sample on surfaces in the absorption cell, effectiveness of mixing when making measurements on mixtures of absorber gas and a buffer gas, and location of the photometric “full-scale” and “zero” levels.