光腔衰荡光谱研究PH2自由基在465-555 nm的光谱

采用光腔衰荡光谱记录了465-555 nm范围内PH₂自由基在射流冷却条件下的吸收光谱. 在超声射流条件下对氩载气中的PH₃和SF₆混合物直流放电产生PH₂自由基. 得到了7个有精细转动结构的振转谱带,并归属为PH₂自由基?²A₁- Χ²B₁电子跃迁的0⁰₀、2ⁿ₀、2ⁿ₁ (n=1-3)跃迁. 在已有的基础上,重新归属每一个振转谱带的转动量子数和转动项值;进一步精细化转动常数、离心畸变常数和自旋转动相互作用常数. 另外还简单讨论了每个K结构受到其它电子态的微扰.     

CW-cavity ringdown spectroscopy of carbon dioxide isotopologues near 1.5 μm

The absorption spectra of carbon dioxide in natural isotopic abundance and with 99% enrichment in ¹³C have been recorded by CW-cavity ringdown spectroscopy in two specific spectral regions: 5957-6122 and 6745-6833 cm⁻¹. The spectra were obtained at Doppler limited resolution by using a CW-CRDS spectrometer based on fibered DFB lasers. The typical sensitivity of 5 × 10⁻¹⁰ cm⁻¹, allowed for the detection of lines with intensity as weak as 5 × 10⁻²⁹ cm/molecule. More than 2900 line positions of the six major isotopologues contributing to the spectra (¹²C¹⁶O₂, ¹⁶O¹²C¹⁷O, ¹⁶O¹²C¹⁸O, ¹³C¹⁶O₂, ¹⁶O¹³C¹⁷O and ¹⁶O¹³C¹⁸O), were measured and assigned on the basis of their respective global effective Hamiltonian models. For comparison, only 507 lines are provided by the HITRAN database in these spectral regions. The band by band analysis has led to the determination of the rovibrational parameters of a total of 52 bands, 30 of them being newly reported. Most of the observed line positions show an agreement close to the experimental uncertainty (1-2 × 10⁻³ cm⁻¹) with the predictions of their respective effective Hamiltonian models. However, the quality of the predictions degrades for the minor isotopologues reaching maximum deviations of 0.35 cm⁻¹ in one specific case. For several bands, rovibrational transitions with J values between 60 and 90 could be newly detected. While an excellent agreement is observed with the line positions predicted by the Hamiltonian models, the comparison of these observations with the line positions listed in the HITRAN database or extrapolated by using the best FTS rotational constants available in the literature has evidenced significant deviations.     

Doppler-limited CW infrared cavity ringdown spectroscopy of the ν1+ν3 OH + CH stretch combination band of jet-cooled methanol

A high resolution cavity ringdown spectrometer (CRDS) has been constructed using a 1.5 μm continuous-wave external-cavity tunable diode laser, a mode-matched near-confocal ringdown cavity, and 2 cm pulsed slit jet. Without signal averaging, the RMS noise in the absorption signal is 1.7 × 10⁻⁹ cm⁻¹. The rotationally resolved overtone spectrum of the OH(ν₁) + CH(ν₃) stretch combination band of methanol between 6510 and 6550 cm⁻¹ has been observed for J^′=0-8 and K^′=0-3 at sub-Doppler resolution. In total, 418 lines are assigned and global fits yield molecular torsion-rotation parameters for the upper state. Four K^′-localized perturbations are analyzed and the pattern of residuals is discussed.     

The ν1 + 3ν2 + 3ν3 and 4ν1 + ν2 + ν3 bands of ozone by CW-cavity ring down spectroscopy between 5900 and 5960 cm

The absorption spectrum of ozone, ¹⁶O₃, has been recorded in the 5903-5960 cm⁻¹ region by high sensitivity CW-cavity ring down spectroscopy (α_min ∼ 5 × 10⁻¹⁰ cm⁻¹). The ν₁ + 3ν₂ + 3ν₃ and 4ν₁ + ν₂ + ν₃ A-type bands centred at 5919.15 and 5947.07 cm⁻¹ were newly observed. A set of 173 and 168 energy levels could be experimentally determined for the (1 3 3) and (4 1 1) states, respectively. Except for a few K_a = 5 levels of the (4 1 1) state, the rotational structure of the two states was found mostly unperturbed. The spectroscopic parameters were determined from a fit of the corresponding line positions by considering the (1 3 3) and (4 1 1) states as isolated. The determined effective Hamiltonian and transition moment operators were used to generate a list of 785 transitions given as Supplementary Material.     

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.     

Temperature and pressure effects on formation and decomposition of phenylvinylperoxy radicals in the C6H5C2H2 + O2 reaction

The effects of temperature and pressure on the formation and decomposition of C₆H₅C₂H₂O₂ in the C₆H₅C₂H₂ + O₂ reaction have been investigated at temperatures from 298 to 378 K by directly monitoring the C₆H₅C₂H₂O₂ radical in the visible region by cavity ringdown spectrometry (CRDS). The rate constant for the C₆H₅C₂H₂ + O₂ association and that for fragmentation of C₆H₅C₂H₂O₂ were found to be k₁ (C₆H₅C₂H₂ + O₂ → C₆H₅C₂H₂O₂) = (3.20 ± 1.19) × 10¹¹ exp(+760/T) cm³ mol⁻¹ s⁻¹ and k₂ (C₆H₅C₂H₂ O₂ → C₆H₅CHO + HCO) = (1.68 ± 0.13) × 10⁴ s⁻¹, respectively. Additional kinetic measurements by pulsed laser photolysis/mass spectrometry show that C₆H₅CHO was produced in the C₆H₅C₂H₂ + O₂ reaction as predicted and the formation of C₆H₅CHO from the decomposition of C₆H₅C₂H₂O₂ is temperature-independent, consistent with the CRDS experimental data.     

The AB2-XA1 electronic transition of NO2: A rovibronic survey covering 14 300-18 000 cm

More than 250 rotationally resolved vibrational bands of the A²B₂-X²A₁ electronic transition of ¹⁵NO₂ have been observed in the 14 300-18 000 cm⁻¹ range. The bands have been recorded in a recently constructed setup designed for high resolution spectroscopy of jet cooled molecules by combining time gated fluorescence spectroscopy and molecular beam techniques. The majority of the observed bands has been rotationally assigned and can be identified as transitions starting from the vibrational ground state or from vibrationally excited (hot band) states. An exceptionally strong band is located at 14 851 cm⁻¹ and studied in more detail as a typical benchmark transition to monitor ¹⁵NO₂ in atmospheric remote sensing experiments. Standard rotational fit routines provide band origins, rotational and spin rotation constants. A subset of 177 vibronic levels of ²B₂ vibronic symmetry has been analyzed in the energy range between 14 300 and 17 250 cm⁻¹, in terms of integrated density and using Next Neighbor Distribution. It is found that the overall statistical properties and polyad structure of ¹⁵NO₂ are comparable to those of ¹⁴NO₂ but that the internal structures of the polyads are completely different. This is a direct consequence of the X²A₁-A²B₂ vibronic mixing.     

High sensitivity cavity ring down spectroscopy of CO2 overtone bands near 790 nm

The dyad bands of near 790 nm have been recorded with a continuous-wave cavity ring-down spectrometer. Two cold bands and the two associated hot bands are observed in this region. High sensitivity of the 1×10⁻¹⁰/cm level allows one to detect weak transitions with satisfied accuracy. The absolute line intensities have also been retrieved with an estimated accuracy of 2% for majority of the unblended lines. The vibrational transition dipole moment squared values and the empirical Herman-Wallis coefficients are presented for two cold bands. The comparison of the retrieved line positions and intensities with those given in the Carbon Dioxide Spectroscopic Databank shows clear deviation and indicates the empirical calculation can be further improved using the present spectroscopy data.     

Surface chemistry of NO and NO2 on the Pt(1 1 0)-(1 × 2) surface: A comparative study

The surface chemistry of NO and NO₂ on clean and oxygen-precovered Pt(1 1 0)-(1 × 2) surfaces were investigated by means of high resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). At room temperature, NO molecularly adsorbs on Pt(1 1 0), forming linear NO(a) and bridged NO(a). Coverage-dependent repulsive interactions within NO(a) drive the reversible transformation between linear and bridged NO(a). Some NO(a) decomposes upon heating, producing both N₂ and N₂O. For NO adsorption on the oxygen-precovered surface, repulsive interactions exist between precovered oxygen adatoms and NO(a), resulting in more NO(a) desorbing from the surface in the form of linear NO(a). Bridged NO(a) experiences stronger repulsive interactions with precovered oxygen than linear NO(a). The desorption activation energy of bridged NO(a) from oxygen-precovered Pt(1 1 0) is lower than that from clean Pt(1 1 0), but the desorption activation energy of linear NO(a) is not affected by the precovered oxygen. NO₂ decomposes on Pt(1 1 0)-(1 × 2) surface at room temperature. The resulted NO(a) (both linear NO(a) and bridged NO(a)) and O(a) repulsively interact each other. Comparing with NO/Pt(1 1 0), more NO(a) desorbs from NO₂/Pt(1 1 0) as linear NO(a), and both linear NO(a) and bridged NO(a) exhibit lower desorption activation energies. The reaction pathways of NO(a) on Pt(1 1 0), desorption or decomposition, are affected by their repulsive interactions with coexisting oxygen adatoms.     

Influence of overcoat on laser-induced damage threshold of 532 and 800 nm TiO2/SiO2 high reflectors

TiO₂/SiO₂ high reflectors with and without a SiO₂ overcoat are deposited by electron-beam evaporation. The film properties are characterized by visible spectrometry measures, structure analysis, roughness and laser-induced damage threshold (LIDT) tests, surface defects and damage morphology observation. The effects of overcoats on LIDT at 532 nm, 8 ns and 800 nm, 220 ps laser pulses are investigated. The relations between film structure, roughness, surface defects, electric field and LIDT are discussed. It is found that overcoats can increase the LIDT at these two laser wavelengths. The reduction of peak temperature, the low defects density and roughness, the low intrinsic absorption of SiO₂ and its amorphous structure are the main reasons for LIDT improvement by overcoats.     

Characterization of single-crystalline In2O3 films deposited on Y-stabilized ZrO2 (1 0 0) substrates by MOCVD

Epitaxial In₂O₃ films have been deposited on Y-stabilized ZrO₂ (YSZ) (1 0 0) substrates by metalorganic chemical vapor deposition (MOCVD). The films were deposited at different substrate temperatures (450-750 °C). The film deposited at 650 °C has the best crystalline quality, and observation of the interface area shows a clear cube-on-cube epitaxial relationship of In₂O₃(1 0 0)||YSZ(1 0 0) with In₂O₃[0 0 1]||YSZ[0 0 1]. The Hall mobility of the single-crystalline In₂O₃ film deposited at 650 °C is as high as 66.5 cm² V⁻¹ s⁻¹ with carrier concentration of 1.5 × 10¹⁹ cm⁻³ and resistivity of 6.3 × 10⁻³ Ω cm. The absolute average transmittance of the obtained films in the visible range exceeds 95%.     

使用发射光谱对感应耦合CF4/CH4等离子体中C2基团形成机理的研究

利用强度标定的发射光谱法，研究了感应耦合CF4₄/CH4₄等离 子体中空间基团的 相对密度随宏观条件（射频输入功率、气压和流量比）的变化情况. 研究表明：在所研究的 碳氟/碳氢混合气体放电等离子体中除了具有丰富的CF，CF2₂，CH，H和F等活 性基团外 ，还同时存在着C2₂基团，其相对密度随着放电功率的提高而增加；随着气压 的上升呈 现倒“U”型的变化. C2₂随流量比R（R=［CH4 _{关键词： 发射光谱 感应耦合等离子体 2}基团')" href="#">C2₂基团     

A (nearly) complete experimental linelist for CO2, OCO, OCO, CO2 and OCO by high-sensitivity CW-CRDS spectroscopy between 5851 and 7045 cm

An experimental database for the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁸O, ¹⁶O¹³C¹⁷O, ¹³C¹⁸O₂ and ¹⁷O¹³C¹⁸O isotopologues of carbon dioxide has been constructed on the basis of the high-sensitivity absorption spectrum of carbon dioxide with 99% enrichment in ¹³C recorded by CW-cavity ring down spectroscopy (CW-CRDS) between 5851 and 7045 cm⁻¹. As a result of the achieved sensitivity (typical noise equivalent absorption α_min∼2-5×10⁻¹⁰ cm⁻¹) combined with the high linearity and dynamics (more than four decades) of the CW-CRDS technique, the amount of spectroscopic information contained in these spectra was considerable. A total of 8639 transitions of the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁸O, ¹⁶O¹³C¹⁷O, ¹³C¹⁸O₂ and ¹⁷O¹³C¹⁸O isotopologues with line strength as low as 5×10⁻²⁹ cm/molecule were assigned. They belong to a total of 150 bands, while less than 20 bands were previously reported by Fourier transform spectroscopy. The excellent agreement between the predictions of the effective operators model and the observations has allowed using an automatic search program to assign the weaker lines observed in the congested spectrum. The spectroscopic parameters of the vibrational upper levels were obtained from a fit of the measured line positions. A number of resonance interactions were observed; in particular, several occurrences of interpolyad anharmonic couplings not included in the polyad model of effective Hamiltonian, were found to affect a few bands of the ¹⁶O¹³C¹⁸O and ¹⁶O¹³C¹⁷O isotopologues. In the list of 8639 transitions, which are provided as Supplementary material, line positions are experimental values (typical uncertainty in the order of 1×10⁻³ cm⁻¹), while line strengths were calculated at 296 K by using the effective operators approach (typical uncertainty in the order of 5%). In the case of the ¹³C¹⁶O₂ isotopologue, the reported transitions represent 99.65% of the total absorbance in the region considered.     

CO2 adsorption on Cr(1 1 0) and Cr2O3(0 0 0 1)/Cr(1 1 0)

We attempt to correlate qualitatively the surface structure with the chemical activity for a metal surface, Cr(1 1 0), and one of its surface oxides, Cr₂O₃(0 0 0 1)/Cr(1 1 0). The kinetics and dynamics of CO₂ adsorption have been studied by low energy electron diffraction (LEED), Aug er electron spectroscopy (AES), and thermal desorption spectroscopy (TDS), as well as adsorption probability measurements conducted for impact energies of E_i = 0.1-1.1 eV and adsorption temperatures of T_s = 92-135 K. The Cr(1 1 0) surface is characterized by a square shaped LEED pattern, contamination free Cr AES, and a single dominant TDS peak (binding energy E_d = 33.3 kJ/mol, first order pre-exponential 1 × 10¹³ s⁻¹). The oxide exhibits a hexagonal shaped LEED pattern, Cr AES with an additional O-line, and two TDS peaks (E_d = 39.5 and 30.5 kJ/mol). The initial adsorption probability, S₀, is independent of T_s for both systems and decreases exponentially from 0.69 to 0.22 for Cr(1 1 0) with increasing E_i, with S₀ smaller by ∼0.15 for the surface oxide. The coverage dependence of the adsorption probability, S(Θ), at low E_i is approx. independent of coverage (Kisliuk-shape) and increases initially at large E_i with coverage (adsorbate-assisted adsorption). CO₂ physisorbs on both systems and the adsorption is non-activated and precursor mediated. Monte Carlo simulations (MCS) have been used to parameterize the beam scattering data. The coverage dependence of E_d has been obtained by means of a Redhead analysis of the TDS curves.     

Density functional theory study into the adsorption of CO2, H and CHx (x = 0-3) as well as C2H4 on α-Mo2C(0 0 0 1)

The structures and energetics of the chemisorbed CO₂, CH_x species and H as well as C₂H₄ on the α-Mo₂C(0 0 0 1) surface have been computed at the GGA-RPBE level of density functional theory. It is found that CO₂ adsorbs dissociately into CO and O, in agreement with the experimental finding. The adsorbed O, CH_x and H species prefer the site of three surface molybdenum atoms over a second layer carbon atom (V_C site). On the basis of the calculated adsorption energies of CH_x and H, the sequential dehydrogenation of CH₄ and the C/C coupling reaction of CH_x have been discussed.     

Air-broadening coefficients of the HO2 radical in the 2ν1 band measured using cw-CRDS

In this paper we present measurements of the air-broadening coefficients of HO₂ at room temperature in the 2ν₁ band around 1.5 microns. The HO₂ radicals were created by flash photolysis of SOCl₂ in a flow of O₂/CH₃OH mixtures. To observe air-broadening, N₂ (79%) and O₂ (21%) were added using calibrated flow controllers and a total pressure controller. The total pressure was monitored in parallel using a capacitive pressure gauge. Air-broadening coefficients at 296 K were determined for 34 absorption lines between 6631 and 6671 cm⁻¹. The air-broadening coefficients of HO₂ show a rotational dependence (decreasing from about 0.14 cm⁻¹/atm for N″ = 3 to about 0.09 cm⁻¹/atm for N″ = 10). No evidence for collisional narrowing was observed.     

CW-cavity ring down spectroscopy of the ozone molecule in the 6220-6400 cm region

The absorption spectrum of ozone,¹⁶O₃, has been recorded in the 6220-6400 cm⁻¹ region by high sensitivity CW-cavity ring down spectroscopy (α_min ∼ 3 × 10⁻¹⁰ cm⁻¹). 1836 rovibrational transitions have been assigned to the 2ν₂ + 5ν₃, 5ν₁ + ν₃ and 2ν₁ +  2ν₂ + 3ν₃ A-type bands centred at 6305, 6355 and 6387 cm⁻¹, respectively. In addition, 99 lines of the very weak ν₁ + 2ν₂ +  4ν₃ and 4ν₁ + 3ν₂ B-type bands are identified. The modeling of the observed spectrum in the effective Hamiltonian approach was particularly laborious and complex as several rovibrational interactions of both Coriolis and anaharmonic type were found to be of importance, in particular for the (124) vibrational state. Nevertheless, it has finally been possible to fit the 990 experimentally determined energy levels with an rms deviation of 8.29 × 10⁻³ cm⁻¹ and to derive the transition moment parameters allowing a satisfactory reproduction of the observed intensities. As the differences in positions between the final calculations and observations are still larger than the experimental accuracy, we provide the list of all energy levels derived from the observation, in addition to their differences with the calculated ones. These experimental energy levels, with the transition moment parameters were used to generate a line-list of 2451 transitions, reproducing the observed spectrum. This list is given as Supplementary Material.     

Electronic band structure and Fermi surface of new low-temperature Ni-based superconductors: 3.3 K (Ni2P2)(Sr4Sc2O6) and 2.7 K (Ni2As2)(Sr4Sc2O6) from first principles

Based on first-principle FLAPW-GGA calculations, we have investigated structural and electronic properties of the recently synthesized tetragonal (space group P4/nmm) nickel-based pnictide oxide superconductors: 3.3 K (Ni₂P₂)(Sr₄Sc₂O₆) and 2.7 K (Ni₂As₂)(Sr₄Sc₂O₆). Optimized structural data, electronic bands, total and partial densities of states, and Fermi surface topology have been obtained and discussed in comparison with available experiments and with their Fe-based (Fe₂P₂)(Sr₄Sc₂O₆) and (Fe₂As₂)(Sr₄Sc₂O₆) analogs.     

Simulation of thermal desorption spectra of N2 observed during N2O decomposition on Rh(1 0 0)

Our measurements indicate that under temperature-programmed conditions the N₂O decomposition occurs on Rh(1 0 0) between 60 and 140 K and results in the appearance of two N₂ desorption peaks related to N₂ molecules leaving the surface during and after N₂O dissociation events, respectively. Both peaks are observed even at low initial coverages. This and other features of N₂ desorption are explained by using Monte Carlo simulations taking into account attractive N₂O-O lateral interactions stabilizing N₂O adsorption. The results presented are compared with those obtained earlier for Rh(1 1 0).     

High sensitivity CW-cavity ring down spectroscopy of N2O near 1.5 μm (I)

The absorption spectrum of nitrous oxide, N₂O, in natural isotopic abundance has been recorded by CW-Cavity Ring Down Spectroscopy between 6000 and 6833 cm⁻¹. The spectra were obtained at Doppler limited resolution by using a CW-CRDS spectrometer based on a series of fibered DFB lasers. The typical sensitivity of 2 × 10⁻¹⁰ cm⁻¹, allowed for the detection of lines with intensity as weak as 2 × 10⁻²⁹ cm/molecule while the minimum intensity value provided by HITRAN in the considered spectral region is 2 × 10⁻²⁵ cm/molecule. More than 6000 line positions of five isotopologues contributing to the spectra (¹⁴N₂¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁴N¹⁵N¹⁶O, ¹⁴N₂¹⁸O and ¹⁴N₂¹⁷O), were measured with a typical accuracy of 1.5 × 10⁻³ cm⁻¹ and rovibrationally assigned on the basis of their respective global effective Hamiltonian models. Highly excited rovibrational levels corresponding to J values larger than 80 could be detected for the stronger vibrational bands. The band by band analysis led to the determination of the rovibrational parameters of a total of 68 bands, 49 of them being newly reported. The rms value of the deviations of the predictions of the effective Hamiltonian models from the observed line positions is 0.010 cm⁻¹. As expected, the quality of the predictions degrades for the minor isotopologues for which important deviations up to a few wavenumbers were evidenced. Most of the bands were found unperturbed but in a few cases, local rovibrational perturbations were evidenced. The interaction mechanisms and the perturbers were univocally assigned on the basis of the effective Hamiltonian model. In particular, interpolyad couplings were evidenced indicating that the polyad version of the effective Hamiltonian has to be extended to include Coriolis and interpolyad anharmonic interactions.