Predissociation of the Schumann-Runge bands of O2

The predissociation line broadening in the Schumann-Runge bands of O₂ is interpreted through an ab initio calculation of the pertinent repulsive potential energy curves and spin-orbit matrix elements. The ab initio results provide an overall qualitative picture of the predissociation which is further refined through a detailed comparison of calculated level shifts and widths with experimental data. The position of the dominant repulsive curve is also deduced by a deperturbation of the level shift in the second vibrational difference. The predissociation is dominated by the ⁵Π_u state crossing the $\text{B}{}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{?}}$ state around 1.875 Å with a spin-orbit matrix element of 65 cm^?1. The ¹Π_u and ³Π_u states have small spin-orbit matrix elements and play only minor roles in the predissociation. The calculated and experimental widths are in good agreement for low and high vibrational levels. The apparent experimental widths between v = 5 and 11 are shown to be inconsistent with the theoretical analysis, the difference probably being due to line blending.     

Absolute absorption cross-section measurements of Schumann-Runge continuum of O2 at 90 and 295 K

Laboratory measurements of the absorption cross-section of the Schumann-Runge continuum of O₂ at the temperatures 90 and 295 K have been made in the wavelength region 130-175 nm. The absolute absorption cross-sections at the same temperatures have been measured at several discrete wavelengths through the region. The absolute cross-sections of the O₂ continuum have been used to put relative cross-sections on a firm absolute basis throughout the region 130-175 nm. These recalibrated cross-sections are available as numerical compilations.     

Deep-UV high resolution cavity ring-down spectroscopy of the Schumann-Runge bands in O2 and O2 at wavelengths 197-203 nm

With the use of a novel titanium:sapphire laser source delivering, upon fourth harmonic generation, narrowband and tunable radiation in the deep-UV, spectroscopic studies were performed on weak Schumann-Runge bands of oxygen. Improved values for rotational and fine structure molecular parameters for the , v = 0-2 states of ¹⁶O₂ were determined, as well as values for the v = 0-1 states in ¹⁸O₂. Signal detection was accomplished via cavity ring-down spectroscopy.     

High sensitivity cw-cavity ringdown and Fourier transform absorption spectroscopies of CO2

The absorption spectrum of ¹³CO₂ has been recorded by cw-cavity ringdown spectroscopy with a new set up based on fibered DFB lasers. By using a series of 31 DFB lasers, the spectrum of carbon dioxide could be recorded in the 6130-6750 cm⁻¹ region with a typical sensitivity of 5 × 10⁻¹⁰ cm⁻¹. The spectrum has also been recorded between 4400 and 8500 cm⁻¹ with a Fourier transform spectrometer associated with a multi-pass cell (maximum path length of 105 m). The new observations obtained both by FTS and CRDS represent a significant extension of the available data. For instance, more than 4000 line positions were measured and assigned in the CRDS spectrum while only 232 line positions are listed in the HITRAN database. Altogether, the band by band analysis has led to the determination of the rovibrational parameters of 65, 7, and 24 bands for the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁷O, and ¹⁶O¹³C¹⁸O isotopomers, respectively. As some observed line positions show significant deviations from the predictions of the effective Hamiltonian model, the new observed line positions were gathered with the data available in the literature to refine the set of effective Hamiltonian parameters of the ¹³C¹⁶O₂ isotopic species. The refined set of 96 effective Hamiltonian parameters reproduces more than 14 650 line positions of ¹³C¹⁶O₂ with an RMS=0.002 cm⁻¹. A detailed comparison with the line positions retrieved from Venus spectra and the line list provided by HITRAN is also presented and discussed.     

Photolysis rate coefficients in the upper atmosphere: Effect of line by line calculations of the O2 absorption cross section in the Schumann-Runge bands

A line by line (LBL) method to calculate highly resolved O₂ absorption cross sections in the Schumann-Runge (SR) bands region was developed and integrated in the widely used Tropospheric Ultraviolet Visible (TUV) model to calculate accurate photolysis rate coefficients (J values) in the upper atmosphere at both small and large solar zenith angles (SZA). In order to obtain the O₂ cross section between 49,000 and 57,000 cm⁻¹, an algorithm which considers the position, strength, and half width of each spectral line was used. Every transition was calculated by using the HIgh-resolution TRANsmission molecular absorption database (HITRAN) and a Voigt profile. The temperature dependence of both the strength and the half widths was considered within the range of temperatures characteristic of the US standard atmosphere, although the results show a very good agreement also at 79 K. The cross section calculation was carried out on a 0.5 cm⁻¹ grid and the contributions from all the lines lying at ±500 cm⁻¹ were considered for every wavelength. Both the SR and the Herzberg continuums were included. By coupling the LBL method to the TUV model, full radiative transfer calculations that compute J values including Rayleigh scattering at high altitudes and large SZA can now be done. Thus, the J values calculations were performed for altitudes from 0 to 120 km and for SZA up to 89°. The results show, in the J_O2 case, differences of more than ±10% (e.g. at 96 km and 30°) when compared against the last version of the TUV model (4.4), which uses the Koppers and Murtagh parameterization for the O₂ cross section. Consequently, the J values of species with cross sections overlapping the SR band region show variable differences at lower altitudes. Although many species have been analyzed, the results for only four of them (O₂, N₂O, HNO₃, CFC12) are presented. Due to the fact that the HNO₃ absorption cross section extends up to 350 nm this molecule was used to verify the consistency of the new TUV-LBL at lower altitudes. Thus, it shows differences up to 5.7% at 21 km but 0% in the troposphere. Because of the more accurate consideration of the Rayleigh scattering the distribution of the actinic flux in its direct and diffuse components (in the SR bands wavelength interval) is also modified.     

Autoionization of O2 by photoelectron spectroscopy

Photoelectron spectra of molecular oxygen have been studied at photon wavelengths of 736, 744 and 584 Å, respectively. The reported strong perturbation at 736 Å leading to changes in the normal vibrational intensifies of the X² Π_g and a⁴Π_u states is ascribed to autoionization from a very wide, near-repulsive state of the neutral molecule. The values measured for the relative vibrational intensifies of the ionic states are compared with the latest experimental results available in the literature.     

Rotational analysis of the 7390- and 7937-Å bands of NO2 by means of Fourier transform spectroscopy

We have extended to higher N and to K_a = 3 and 4 the rotational analysis of the 7390-Å band of NO₂ performed by K. E. Hallin and A. J. Merer (Canad. J. Phys.55, 2101–2112 (1977)). The lines belong to a perturbed parallel band for which Hallin and others have proposed the vibrational assignment (2 13 1)-(0 0 0) within the electronic ground state. These authors presumed that this band borrows its intensity through a vibronic coupling (spin-orbit and/or Coriolis coupling) from the stronger (0 2 0)-(0 0 0) band of the $\text{A}\text{?}\text{-}\text{X}\text{?}$ electronic system at 7460 Å. We have observed about 900 transitions belonging to the K_a = 0, 1, 2, 3, 4 subbands of the (2 13 1)-(0 0 0) band for N values going up to about 23, and 300 lines of the “hot” band (2 13 1)-(0 1 0). We have also looked for spin-orbit-induced transitions and we have detected about 400 transitions with ΔN ≠ ΔJ. Among them ΔN = ±2 transitions with ΔK_a = 0 or ± 2 have been observed, indicating that N and K_a are no longer good quantum numbers, and demonstrating clearly the existence of rovibronic interactions perturbing the upper levels of the transitions.     

机载腔增强吸收光谱系统应用于大气NO_2空间高时间分辨率测量

介绍了一套用于机载平台测量的非相干宽带腔增强吸收光谱(IBBCEAS)系统,并应用于实际大气NO_2空间分布的高时间分辨率观测.为满足机载测量中对时间分辨率的需求,系统采用离轴抛物面镜代替消色差透镜提高光学耦合效率;并运用Allan方差,对系统性能进行了分析.通过腔增强吸收光谱系统与长光程吸收光谱系统对实际大气NO_2的对比测试,两者线性相关系数R~2达到0.86.将IBBCEAS系统应用于机载平台,在时间分辨率为2 s的情况下,探测限达到95 ppt(1σ).通过机载观测,获得了华北地区石家庄等地上空对流层大气NO_2的廓线信息.     

Investigation of collision-induced absorption in the vibrational fundamental bands of O2 and N2 at elevated temperatures

Collision-induced absorption has been measured for the vibrational fundamental bands of N₂ and O₂ at temperatures up to 360 K. These data when combined with previously obtained lower temperature data show that the integrated band intensity of the O₂ fundamental increases as the temperature is raised above 300 K. The integrated intensity of the N₂ band also increases, but at a much lower rate with temperature.     

Al2O3-Y2O3-ZrO2三相复合陶瓷的介电谱研究

采用传统的固相反应法,在1400–1500 ℃下烧结,制备得到Al₂O₃-Y₂O₃-ZrO₂三相复合陶瓷.样品的结构、形貌和电性能分别用X射线衍射(XRD)、扫描电子显微镜(SEM)及介电谱表征.XRD表明此三相复合体系无其他杂相,加入Y₂O₃及ZrO₂后使得Al₂O₃成瓷温度降低;SEM表明此体系晶粒直径为200–500 nm,并且样品随烧结温度的升高而变得更加致密,晶界更加清晰;介电损耗谱中出现峰值弛豫现象,根据Cole-Cole复阻抗谱得出其为非德拜弛豫. 关键词： 2O₃-Y₂O₃-ZrO₂三相陶瓷')" href="#">Al₂O₃-Y₂O₃-ZrO₂三相陶瓷 介电弛豫 阻抗谱 热导率     

Ground-based photon path measurements from solar absorption spectra of the O2 A-band

High-resolution solar absorption spectra obtained from Table Mountain Facility (TMF, 34.38°N, 117.68°W, 2286 m elevation) have been analyzed in the region of the O₂ A-band. The photon paths of direct sunlight in clear sky cases are retrieved from the O₂ absorption lines and compared with ray-tracing calculations based on the solar zenith angle and surface pressure. At a given zenith angle, the ratios of retrieved to geometrically derived photon paths are highly precise (0.2%), but they vary as the zenith angle changes. This is because current models of the spectral lineshape in this band do not properly account for the significant absorption that exists far from the centers of saturated lines. For example, use of a Voigt function with Lorentzian far wings results in an error in the retrieved photon path of as much as 5%, highly correlated with solar zenith angle. Adopting a super-Lorentz function reduces, but does not completely eliminate this problem. New lab measurements of the lineshape are required to make further progress.     

基于O2-O2吸收的非相干宽带腔增强吸收光谱浓度反演方法研究

针对传统非相干宽带腔增强吸收光谱浓度反演方法的定量结果易受镜片反射率标定误差的影响问题, 提出了一种基于测量大气O₂-O₂吸收的浓度反演方法. 该方法是将非相干宽带腔增强吸收光谱技术的光学增强腔等效成吸收光程不随波长变化的多次反射池, 首先根据测得的宽带腔增强大气吸收谱和参考谱计算出光学厚度, 并应用差分光学吸收光谱算法拟合修正后的气体吸收截面到光学厚度, 反演得到大气中O₂-O₂以及被测气体的柱浓度, 然后根据O₂-O₂在大气中的含量已知且相对稳定这一特性, 确定出等效多次反射池的吸收光程, 最后从被测气体的柱浓度中扣除吸收光程信息得到被测气体的浓度值. 以监测大气中NO₂实验为例, 应用该方法在454-487 nm波段反演得到了大气NO₂的浓度(1-30 ppbv范围内), 并将反演结果与传统浓度反演方法的结果进行了对比, 发现两者的不一致性在7%以内. 实验结果表明, 非相干宽带腔增强吸收光谱技术可以利用大气O₂-O₂的吸收来定量其他被测气体的浓度, 而且定量结果对镜片反射率的标定误差不敏感.     

Aerosol influence on polarization and intensity in near-infrared O2 and CO2 absorption bands observed from space

We study the intensity and degree of linear polarization of reflected solar radiation at the top of the atmosphere within two carbon dioxide bands and one oxygen absorption band in the near-infrared. In particular, we are interested in the sensitivity of the degree of linear polarization and intensity to changes of aerosol and cirrus cloud layer heights, microphysical properties, and surface albedo. For the simulations we use spectral response functions representative of the Orbiting Carbon Observatory (OCO). Inside the O₂A band at 760 nm and strong CO₂ band at 2060 nm we find a strong influence of the aerosol and cirrus cloud layer height on the degree of linear polarization. An increase of the aerosol or cirrus cloud layer height can lead either to a decrease or increase of the polarization within the band, depending on the microphysical and optical properties of the scatterers, surface albedo, and absorption strength in the bands. The results for the O₂A band also indicate that even over land OCO enables an estimation of the height of an aerosol or cirrus cloud layer. Inside the weak CO₂ band at 1610 nm the influence of aerosol or cirrus cloud layer heights is lower as compared to the O₂A band and CO₂ band at 2060 nm, due to the relatively stronger surface influence. Here an increase of aerosol or cirrus cloud layer height leads to an increase of the degree of linear polarization even in case of low surface albedo and for weakly polarizing scatterers. For the weak CO₂ band at 1610 nm we also study the influence of the aerosol or cirrus cloud layer height on the column CO₂ estimate and the errors resulting from ignoring polarization in simulations of backscatter measurements by space-based instruments such as OCO. Depending on the surface albedo, misinterpretations of the height of atmospheric scatterers might strongly affect the column CO₂ estimates.     

Predissociation linewidths and oscillator strengths for the (2-0) to (13-0) Schumann-Runge bands of O2

Analysis of the absorption spectrum of O₂ in the Schumann-Runge bands (B³Σ_u^?-X³Σ_g^?) from the 2-0 to the 13-0 band yields oscillator strengths which are in good agreement with past theoretical calculations. Predissociation linewidths deduced from the data tend to be larger than theoretical predictions for v′ ≤ 5 and are reasonably near theory for v′ > 5. The qualitative dependence of the linewidths on vibrational level is in accord with that expected for a repulsive potential intersecting the B³Σ state near v′ = 4. For a given band the predissociation linewidth deduced from the spectra tends to increase as the total angular momentum increases. The new linewidths are smaller than some past experimental results, and this will have an impact on future calculations of the photodissociation rates of O₂, NO, and H₂O in the earth's upper atmosphere.     

High resolution cw CARS spectroscopy in D2 gas

The result of spectroscopic measurements of the Q-branch of gaseous D₂ by the method of coherent anti-Stokes Raman scattering are presented. The experiments were carried out with cw single-frequency lasers. The resolution was 40 MHz. The dispersion of |χ⁽³⁾| was investigated and its maximum value was estimated to be (0.7 ± 0.3) × 10^-13 esu at 1 atm pressure. The full width of Q(2) line versus pressure was measured over the range of 0.06–40 atm. Signal to noise ratios reached 10⁵ in our experiments.     

The ν9 band of diazirine,H2CN2, by Doppler-limited Fourier transform infrared spectroscopy

The Doppler-limited infrared spectrum of diazirine was recorded using a high-information Fourier transform spectrometer with a resolution of 0.0054 cm^?1. The rovibrational structure of the ν₉ fundamental (CH₂ rocking) at 1124.9144 cm^?1, which is a C-type band, was analyzed in detail with extensive use of spectrum simulation and correlation diagrams. The molecular constants for the upper energy level of this band were obtained from the overall rovibrational assignment of more than 2000 transitions, which cover the region from 1070 to 1220 cm^?1.     

Fourier transform and CARS spectroscopy of the ν1 and ν3 fundamental bands of 14NH3

The ν₁ and ν₃ fundamental bands of ¹⁴NH₃ have been measured using the techniques of Fourier transform and coherent anti-Stokes Raman spectroscopy. The effective values of the band origins, rotational and centrifugal distortion constants, and parameters of the vibrational-rotational interactions have been obtained by analyzing these bands as essentially regular parallel and perpendicular bands, with the “off-diagonal” local resonance interactions excluded from the fit. The “diagonal” l-type resonance effects have been included into the analysis of the ν₃ band for the +l, K = 1 and ?l, K = 2 levels.     

Wing profile measurements of the Na-doublet lines in C2H2/O2/N2, H2/O2/N2 and H2/O2/Ar frames at 1 atm

Fluorescence-excitation (wing) profiles of the Na-D doublet lines were measured over a wavelength range extending from 0.3 to 200 Å from the line center for the red D₁ and blue D₂ wings and from 0.3 to 3 Å for the red D₂ and the blue D₁ wings, respectively. The line profiles were determined with the aid of a tunable CW dye-laser as a background source by measuring the total fluorescence intensity observed on detuning the laser wavelength. The flames were premixed, laminar, shielded flames at 1 atm, with temperatures ranging from 1860 to 2270 K; N₂ and Ar served as diluent gases. The line core and near-wing profiles (i.e. the region covering 0.3<Δλ<7 Å for the outer wings and 0.3<Δλ<3 Å for the inner ones) in all of the flames studied appeared to have the same frequency dependence, regardless of the nature and concentrations of the gases used. The blue D₂-line profile followed an unexpected (-2.2) law, while the other three profiles obeyed the theoretically expected (-2) law (the dispersion profile function). The line profile in the Δλ range between the impact and quasistatic regions was found to depend on the main perturbers involved. We found that the far blue D₂- and red D₁-wings in the Ar-diluted H₂/O₂ flame obeyed the (-$\text{5}\text{4}$) and (-$\text{3}\text{2}$) laws, respectively, as predicted by the quasi-static theory for the Lennard-Jones interaction. For the N₂-diluted C₂H₂/O₂ and H₂/O₂ flames, we did not find these wing dependences in the Δλ range investigated.     

High resolution studies of NiSi2 ultrathin film formation by ion scattering and cross-section tem

Ultrathin epitaxial NiSi₂ films (0–40 Å) have been grown on Si(111) surfaces. Medium energy ion shadowing and blocking has been used to determine the orientation, morphology and interfacial order of these films. For the whole coverage range studied ((0–1) × 10¹⁶ Ni $\text{atoms}\text{cm}{}^2$) the films are found to be rotated 180° about the surface normal with respect to the Si(111) substrate. Using the high depth resolution of the technique the annealed films are shown to consist initially of islands, which coalesce into continuous films for coverages above ≈ 5 × 10¹⁵ Ni $\text{atoms}\text{cm}{}^2$. High resolution cross-section transmission electron microscopy shows the NiSi₂Si interface to be atomically abrupt. This interface has been probed directly using the ion channeling technique, and the number of disordered Ni atoms at the interface is found to be less than 7.5 × 10¹³$\text{atoms}\text{cm}{}^2$.