Infrared Absorption Cross Sections Research Articles

Mechanism of Photo-Oxidation of Heptafluorobutyric Anhydride in the Presence of NO2. Synthesis and Characterization of Heptafluoropropyl Peroxynitrate, CF3CF2CF2OONO2

The photolysis of heptafluorobutyric anhydride at 254 nm in the presence of NO(2) and O(2) has been studied. It leads to the formation of CF(3)CF(2)CF(2)OONO(2), CF(3)CF(2)OONO(2), and CF(2)O as the only fluorine-containing carbonaceous products. The formation of the new heptafluoropropyl peroxynitrate (HFPN, CF(3)CF(2)CF(2)OONO(2)), as one of the main products, is a consequence of the formation of CF(3)CF(2)CF(2)OO(•) radicals followed by the reaction with NO(2). To characterize HFPN, the UV absorption cross sections and their temperature dependence between 245 and 300 K have been measured over the wavelength range 200-300 nm as well as the infrared absorption cross sections. Kinetic parameters for its thermal decomposition are also presented in the temperature range between 281 and 300 K. The Rice-Ramsperger-Kassel-Marcus calculation reveals that the rate coefficient for the thermal decomposition at 285 K is almost independent of total pressure. The mechanism for the decomposition of CF(3)CF(2)CF(2)OONO(2) in the presence of NO was adjusted by a kinetic model, which enabled the calculation of important rate coefficients.

Temperature-dependent absorption cross-section measurements of 1-butene (1-C4H8) in VUV and IR

Vacuum ultraviolet (VUV) and infrared (IR) absorption cross-section measurements of 1-butene (1-C4H8; CH2=CHCH2CH3; Butylene) are reported over the temperature range of 296–529K. The VUV measurements are performed between 115 and 205nm using synchrotron radiation as a tunable VUV light source. Fourier Transform Infrared (FTIR) spectroscopy is employed to measure absorption cross-section and band strengths in the IR region between 1.54 and 25μm (∼6500–400cm−1). The measured room-temperature VUV and IR absorption cross-sections are compared with available literature data and are found to be in good agreement. The oscillator strength for the electronic transition (A1A′→X1A′) around 150–205nm is determined to be 0.32±0.01.The gas temperature has a strong effect on both VUV and IR spectra. Measurements made in the VUV region show that the peak value of the band cross-section decreases and the background continuum increases with increasing gas temperature. This behavior is due to a change in the rotational and vibrational population distribution of 1-butene molecule. Similar changes in rotational population are observed in the IR spectra. Moreover, variation of the IR spectra with temperature is used to measure the enthalpy difference between syn and skew conformations of 1-butene and is found to be 0.24±0.03kcal/mol, which is in excellent agreement with values reported in the literature. The measurements reported in this work will provide the much-needed spectroscopic information for the development of high-temperature quantitative diagnostics in combustion applications and validation of atmospheric chemistry models of extra-solar planets.

Infrared absorption cross sections for methanol

Infrared absorption cross sections for methanol, CH3OH, have been determined near 3.4 and 10μm from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125HR) and a multipass cell with a maximum optical path length of 19.3m. Methanol/dry synthetic air mixtures were prepared and spectra were recorded at 0.015cm−1 resolution (calculated as 0.9/MOPD) at a number of temperatures and pressures (50–760Torr and 204–296K) appropriate for atmospheric conditions. Intensities were calibrated using composite methanol spectra taken from the Pacific Northwest National Laboratory (PNNL) IR database. The new measurements in the 10μm region indicate problems with the existing methanol spectroscopic line parameters in the HITRAN database, which will impact the accuracy of satellite retrievals.

Measurements of the infrared absorption cross-sections of HCFC-141b (CH3CFCl2)

Detection of atmospheric trace gases by optical remote sensing techniques relies on the availability of molecular absorption spectra over a range of relevant temperatures. Absorption cross-sections of a pure vapour of the hydrochlorofluorocarbon HCFC-141b are reported at a resolution of 0.02cm−1 for a range of temperatures between 223 and 283K and a spectral range of 570–3100cm−1. The integrated intensities of the nine main harmonic bands compare well with the data available from previous experimental studies and with theoretical calculations by ab initio and density functional theories.

Temperature dependence of the infrared absorption cross-sections of neutral species commonly found in fluorocarbon plasmas

This article serves as a reference for the analysis of Fourier transform infrared spectroscopy data from processing plasmas. Until now, there has been a lack of accurate reference data for addressing the problems of species identification and density measurements in cases of increasing gas temperatures. Our results show that, while the integrated absorption cross-sections do not change significantly as temperature increases, the temperature of the absorbing species can be estimated from the rotational band maximum in most cases. Integrated absorption cross-sections for c-C3F6, C4F8, C3F8, C2F6, C2F4, and CF4 are presented for all fundamental bands in the 650 cm−1 to 2000 cm−1 region. In addition, the binary combination bands up to 4000 cm−1 are presented for all species. The temperature of each species has been varied to correspond to neutral temperatures commonly found in processing plasmas.

Mid- and long-wave infrared absorption cross sections for acetonitrile

Infrared absorption cross sections for acetonitrile (methyl cyanide; CH 3CN) have been determined in the 880–1700 cm −1 spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125 HR) and a multipass cell with a maximum optical pathlength of 19.3 m. Spectra of acetonitrile/dry synthetic air mixtures were recorded at 0.015 cm −1 resolution (calculated as the Bruker instrument resolution of 0.9/MOPD) at a number of temperatures between 203 and 297 K and pressures appropriate for atmospheric conditions. Intensities were calibrated using three composite acetonitrile spectra recorded at the Pacific Northwest National Laboratory. These absorption cross sections will provide an accurate basis for upper tropospheric/lower stratospheric retrievals of acetonitrile in the mid-infrared spectral region from ACE satellite data.

Acetonitrile (CH 3CN) infrared absorption cross sections in the 3 μm region

High resolution infrared absorption cross sections of acetonitrile have been determined from spectra recorded in the 3 μm spectral region using a Bruker IFS 125 HR Fourier transform spectrometer (FTS) and a multipass White cell. The eleven synthetic air-broadened acetonitrile spectra were recorded at a resolution of 0.015 cm −1 (calculated as 0.9/MOPD (Maximum Optical Path Difference), the Bruker definition of resolution) over a range of different temperatures and pressures that are representative of conditions in the Earth's atmosphere (50–760 Torr and 207–296 K). Intensities were calibrated using infrared spectra recorded at the Pacific Northwest National Laboratory (PNNL). These new cross sections will enable satellite retrievals of acetonitrile in the 3 μm region from atmospheric spectra recorded by satellite instruments, such as the ACE (Atmospheric Chemistry Experiment)-FTS.

Mid-infrared absorption cross-sections and temperature dependence of CFC-113

The temperature dependence of the infrared absorption cross-sections of CFC-113 (1,1,2-trichlorotrifluoroethane) in a pure vapor phase has been recorded in the 600–1250 cm −1 spectral region using Fourier transform spectroscopy. Spectra at 0.05 cm −1 resolution have been used to derive the integrated band strengths of the five main absorption bands over a range of temperatures from 223 to 283 K. Our results show good agreement with previously published data. The new cross-sections will allow more accurate retrieval of atmospheric CFC-113 concentrations using infrared spectroscopic techniques.

Infrared absorption cross-sections for acetaldehyde (CH 3CHO) in the 3 μm region

A series of infrared absorption cross-sections for acetaldehyde has been measured in the 3 μm region from spectra obtained using a high-resolution Fourier transform spectrometer (Bruker IFS 125/HR). Results presented are for mixtures of acetaldehyde vapor combined with pure synthetic air taken at various temperatures and pressure to simulate atmospheric conditions found principally in the Earth's troposphere and lower stratosphere. Spectra were recorded at a resolution of 0.005 cm −1 and intensities were calibrated using three acetaldehyde spectra (measured at 278, 298 and 323 K) provided by the Pacific Northwest National Laboratory (PNNL) IR database.

Mid-infrared absorption cross sections for acetone (propanone)

Infrared absorption cross sections for acetone (propanone) have been determined in the 830–1950 cm −1 spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125HR) and a multipass cell with a maximum optical path length of 19.3 m. The spectra of mixtures of acetone with dry synthetic air were recorded at 0.015 cm −1 resolution (calculated as 0.9/MOPD using the Bruker definition of resolution) at a number of temperatures between 194 and 251 K and pressures appropriate for atmospheric conditions. Intensities were calibrated using three acetone spectra (recorded at 278, 293 and 323 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database. The new absorption cross sections have been combined with previous high spectral resolution results to create a more complete set of acetone absorption cross sections appropriate for atmospheric remote sensing. These cross sections will provide an accurate basis for upper tropospheric/lower stratospheric retrievals of acetone in the mid-infrared spectral region from ACE and MIPAS satellite data.

Infrared absorption cross sections for acetone (propanone) in the 3 μm region

Infrared absorption cross sections for acetone (propanone), CH 3C(O)CH 3, have been determined in the 3 μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125 HR) and a multipass cell with a maximum optical path length of 19.3 m. The spectra of mixtures of acetone with dry synthetic air were recorded at 0.015 cm −1 resolution (calculated as 0.9/MOPD using the Bruker definition of resolution) at a number of temperatures and pressures (50–760 Torr and 195–296 K) appropriate for atmospheric conditions. Intensities were calibrated using three acetone spectra (recorded at 278, 293 and 323 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.

Global Warming Potential of Inhaled Anesthetics

Inhaled anesthetics are recognized greenhouse gases. Calculating their relative impact during common clinical usage will allow comparison to each other and to carbon dioxide emissions in general. We determined infrared absorption cross-sections for sevoflurane and isoflurane. Twenty-year global warming potential (GWP(20)) values for desflurane, sevoflurane, and isoflurane were then calculated using the present and previously published infrared results, and best estimate atmospheric lifetimes were determined. The total quantity of each anesthetic used in 1 minimal alveolar concentration (MAC)-hour was then multiplied by the calculated GWP(20) for that anesthetic, and expressed as "carbon dioxide equivalent" (CDE(20)) in grams. Common fresh gas flows and carrier gases, both air/oxygen and nitrous oxide (N2O)/oxygen, were considered in the calculations to allow these examples to represent common clinical use of inhaled anesthetics. GWP(20) values for the inhaled anesthetics were: sevoflurane 349, isoflurane 1401, and desflurane 3714. CDE(20) values for 1 MAC-hour at 2 L fresh gas flow were: sevoflurane 6980 g, isoflurane 15,551 g, and desflurane 187,186 g. Comparison among these anesthetics produced a ratio of sevoflurane 1, isoflurane 2.2, and desflurane 26.8. When 60% N2O/40% oxygen replaced air/oxygen as a carrier gas combination, and inhaled anesthetic delivery was adjusted to deliver 1 MAC-hour of anesthetic, sevoflurane CDE(20) values were 5.9 times higher with N2O than when carried with air/O2, isoflurane values were 2.9 times higher, and desflurane values were 0.4 times lower. On a 100-year time horizon with 60% N2O, the sevoflurane CDE(100) values were 19 times higher than when carried in air/O2, isoflurane values were 9 times higher, and desflurane values were equal with and without N2O. Under comparable and common clinical conditions, desflurane has a greater potential impact on global warming than either isoflurane or sevoflurane. N2O alone produces a sizable greenhouse gas contribution relative to sevoflurane or isoflurane. Additionally, 60% N2O combined with potent inhaled anesthetics to deliver 1 MAC of anesthetic substantially increases the environmental impact of sevoflurane and isoflurane, and decreases that of desflurane. N2O is destructive to the ozone layer as well as possessing GWP; it continues to have impact over a longer timeframe, and may not be an environmentally sound tradeoff for desflurane. From our calculations, avoiding N2O and unnecessarily high fresh gas flow rates can reduce the environmental impact of inhaled anesthetics.

Infrared absorption cross sections for propane (C 3H 8) in the 3 μm region

Infrared absorption cross sections for propane have been measured in the 3 μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125 HR). The spectra of mixtures of propane with dry synthetic air were recorded at 0.015 cm −1 resolution (calculated as 0.9/MOPD using the Bruker definition of resolution), at a number of temperatures and pressures appropriate for atmospheric conditions. Intensities were calibrated using two propane spectra (recorded at 278 and 293 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.

Temperature-dependent absorption cross-sections of HCFC-142b

Following the recent detection of HCFC-142b (1-chloro-1,1-difluoroethane) from space, laboratory infrared absorption cross-section spectra of this molecule in a pure vapour phase have been recorded in the 650 – 3500 cm - 1 spectral region using Fourier transform spectroscopy. The spectra have been recorded at a resolution of 0.02 cm - 1 and a range of temperatures from 223 to 283 K. The resulting data show good agreement with the harmonic frequencies and intensities calculated using density functional theory as well as with the integrated absorption intensities of the spectral bands available in the literature. The new cross-sections will allow more accurate retrieval of atmospheric HCFC-142b concentrations using infrared spectroscopic techniques.

Infrared absorption cross sections for ethane (C 2H 6) in the 3 μm region

Infrared absorption cross sections for ethane have been measured in the 3 μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125/HR). Results are presented for pure ethane gas from spectra recorded at 0.004 cm −1 resolution and for mixtures with dry synthetic air from spectra obtained at 0.015 cm −1 resolution (calculated as 0.9/MOPD using the Bruker definition of resolution), at a number of temperatures and pressures appropriate for atmospheric conditions. Intensities were calibrated using three ethane spectra (recorded at 278, 293, and 323 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.

Experimental and Theoretical Study of the Atmospheric Chemistry and Global Warming Potential of SO2F2

In this work, potential atmospheric loss processes for SO2F2, a commercially used biocide (fumigant), have been studied and its global warming potential calculated. Rate coefficients for the gas-phase reactions OH + SO2F2 --> products, k1, and Cl + SO2F2 --> products, k4, were determined using a relative rate technique to be k1 < 1 x 10(-16) cm3 molecule-1 s-1 at 296 and 333 K and k4(296 K) < 5 x 10(-17) cm3 molecule(-1) s(-1). UV absorption cross sections of SO2F2 were measured at 184.9, 193, and 213.9 nm, and its photolysis quantum yield at 193 nm was determined to be <0.02. The atmospheric lifetime of SO2F2 with respect to loss by OH, Cl, and O(1D) reaction and UV photodissociation is estimated to be >300, >10000, 700, and >4700 years, respectively. The stratospheric lifetime of SO2F2 is calculated using a two-dimensional model to be 630 years. The global warming potential (GWP) for SO2F2 was calculated to be 4780 for the 100 year time horizon using infrared absorption cross sections measured in this work and a SO2F2 globally averaged atmospheric lifetime of 36 years, which is determined primarily by ocean uptake, reported by Mühle et al. (Mühle, J.; Huang, J.; Weiss, R. F.; Prinn, R. G.; Miller, B. R.; Salameh, P. K.; Harth, C. M.; Fraser, P. J.; Porter, L. W.; Greally, B. R.; O'Doherty, S.; Simonds, P. G. J. Geophys. Res., submitted for publication, 2008). Reaction channels and the possible formation of stable adducts in reactions 1 and 4 were evaluated using ab initio, CCSD(T), and density functional theory, B3P86, quantum mechanical electronic structure calculations. The most likely reaction product channels were found to be highly endothermic, consistent with the upper limits of the rate coefficients measured in this work.

Sub-picosecond time resolved infrared spectroscopy of high-spin state formation in Fe(ii) spin crossover complexes

The photoinduced low-spin (S = 0) to high-spin (S = 2) transition of the iron(ii) spin-crossover systems [Fe(btpa)](PF(6))(2) and [Fe(b(bdpa))](PF(6))(2) in solution have been studied for the first time by means of ultrafast transient infrared spectroscopy at room temperature. Negative and positive infrared difference bands between 1000 and 1065 cm(-1) that appear within the instrumental system response time of 350 fs after excitation at 387 nm display the formation of the vibrationally unrelaxed and hot high-spin (5)T(2) state. Vibrational relaxation is observed and characterized by the time constants 9.4 +/- 0.7 ps for [Fe(btpa)](PF(6))(2)/acetone and 12.7 +/- 0.7 ps for both [Fe(btpa)](PF(6))(2)/acetonitrile and [Fe(b(bdpa)](PF(6))(2)/acetonitrile. Vibrational analysis has been performed via DFT calculations of the low-spin and high-spin state normal modes of both compounds as well as their respective infrared absorption cross sections. The simulated infrared difference spectra are dominated by an increase of the absorption cross section upon high-spin state formation in accordance with the experimental infrared spectra.

CF3CFCH2and (Z)-CF3CFCHF: temperature dependent OH rate coefficients and global warming potentials

Rate coefficients over the temperature range 206-380 K are reported for the gas-phase reaction of OH radicals with 2,3,3,3-tetrafluoropropene (CF(3)CF=CH(2)), k(1)(T), and 1,2,3,3,3-pentafluoropropene ((Z)-CF(3)CF=CHF), k(2)(T), which are major components in proposed substitutes for HFC-134a (CF(3)CFH(2)) in mobile air-conditioning units. Rate coefficients were measured under pseudo-first-order conditions in OH using pulsed-laser photolysis to produce OH and laser-induced fluorescence to detect it. Rate coefficients were found to be independent of pressure between 25 and 600 Torr (He, N(2)). For CF(3)CF=CH(2), the rate coefficients, within the measurement uncertainty, are given by the Arrhenius expression k(1)(T)=(1.26+/-0.11) x 10(-12) exp[(-35+/-10)/T] cm(3) molecule(-1) s(-1) where k(1)(296 K)=(1.12+/-0.09) x 10(-12) cm(3) molecule(-1) s(-1). For (Z)-CF(3)CF=CHF, the rate coefficients are given by the non-Arrhenius expression k(2)(T)=(1.6+/-0.2) x 10(-18)T(2) exp[(655+/-50)/T] cm(3) molecule(-1) s(-1) where k(2)(296 K)=(1.29+/-0.06) x 10(-12) cm(3) molecule(-1) s(-1). Over the temperature range most relevant to the atmosphere, 200-300 K, the Arrhenius expression k(2)(T)=(7.30+/-0.7) x 10(-13) exp[(165+/-20)/T] cm(3) molecule(-1) s(-1) reproduces the measured rate coefficients very well and can be used in atmospheric model calculations. The quoted uncertainties in the rate coefficients are 2sigma (95% confidence interval) and include estimated systematic errors. The global warming potentials for CF(3)CF=CH(2) and (Z)-CF(3)CF=CHF were calculated to be <4.4 and <3.6, respectively, for the 100 year time horizon using infrared absorption cross sections measured in this work, and atmospheric lifetimes of 12 and 10 days that are based solely on OH reactive loss.

Octamethylcyclotetrasiloxane-Based, Low-Permittivity Organosilicate Coatings: Composition, Structure, and Polarizability

Organosilicate glass (OSG) coatings with a range of compositions have been deposited using , He, and octamethylcyclotetrasiloxane as a precursor in a plasma-enhanced chemical vapor deposition process. Rutherford backscattering spectrometry and forward recoil spectrometry were used to determine the composition of the coatings. The measurements show that addition of carbon and hydrogen lowers the density of the coatings, effectively reducing the concentration of the polarizing species. The dielectric constant is further lowered by a reduction of the ionic and orientation polarizabilities. Fourier transform infrared measurements show that as more C and H are incorporated, the siloxane network is more frequently interrupted by terminal methyl and H groups. Based on the experimental results a quantitative model for the OSG structure is proposed and the inverse infrared absorption cross sections of various absorption bands are determined, some of which for the first time. The structural model also makes it possible to calculate the average electronic polarizability of the various bond configurations in the OSG.

Infrared vibrational spectroscopy of cis-dichloroethene in Rydberg states

We have measured the infrared (IR) vibrational spectrum for cis-dichloroethene (cis-ClCH[Double Bond]CHCl) in excited Rydberg states with the effective principal quantum numbers n(*)=9, 13, 17, 21, 28, and 55 using the vacuum ultraviolet-IR-photoinduced Rydberg ionization (VUV-IR-PIRI) scheme. Although the IR frequencies observed for the vibrational bands nu(11) (*) (asymmetric C-H stretch) and nu(12) (*) (symmetric C-H stretch) are essentially unchanged for different n(*) states, suggesting that the IR absorption predominantly involves the ion core and that the Rydberg electron behaves as a spectator; the intensity ratio for the nu(11) (*) and nu(12) (*) bands [R(nu(11) (*)nu(12) (*))] is found to decrease smoothly as n(*) is increased. This trend is consistent with the results of a model ab initio quantum calculation of R(nu(11) (*)nu(12) (*)) for excited cis-ClCH[Double Bond]CHCl in n(*)=3-18 states and the MP26-311++G(2df,p) calculations of R(nu(11)nu(12)) and R(nu(11) (+)nu(12) (+)), where R(nu(11)nu(12))[R(nu(11) (+)nu(12) (+))] represents the intensity ratio of the nu(11)(nu(11) (+)) asymmetric C-H stretching to the nu(12)(nu(12) (+)) symmetric C-H stretching vibrational bands for cis-ClCH[Double Bond]CHCl (cis-ClCH[Double Bond]CHCl(+)). We have also measured the IR-VUV-photoion (IR-VUV-PI) and IR-VUV-pulsed field ionization-photoelectron depletion (IR-VUV-PFI-PED) spectra for cis-ClCH[Double Bond]CHCl. These spectra are consistent with ab initio calculations, indicating that the IR absorption cross section for the nu(12) band is negligibly small compared to that for the nu(11) band. While the VUV-IR-PIRI measurements have allowed the determination of nu(11) (+)=3067+/-2 cm(-1), nu(12) (+)=3090+/-2 cm(-1), and R(nu(11) (+)nu(12) (+)) approximately 1.3 for cis-ClCH=CHCl(+), the IR-VUV-PI and IR-VUV-PFI-PED measurements have provided the value nu(11)=3088.5+/-0.2 cm(-1) for cis-ClCH=CHCl.