Vacuum Ultraviolet Spectra Research Articles

YVO4∶Tm3+的真空紫外发光性能

YVO₄∶Tm³⁺的真空紫外发光性能

VACUUM ULTRAVIOLET EMISSION SPECTRUM MEASUREMENT OF A MICROWAVE-DISCHARGE HYDROGEN-FLOW LAMP IN SEVERAL CONFIGURATIONS: APPLICATION TO PHOTODESORPTION OF CO ICE

We report measurements of the vacuum ultraviolet (VUV) emission spectra of a microwave-discharge hydrogen-flow lamp (MDHL), a common tool in astrochemistry laboratories working on ice VUV photoprocessing. The MDHL provides hydrogen Ly-α (121.6 nm) and H2 molecular emission in the 110-180 nm range. We show that the spectral characteristics of the VUV light emitted in this range, in particular the relative proportion of Ly-α to molecular emission bands, strongly depend on the pressure of H2 inside the lamp, the lamp geometry (F type versus T type), the gas used (pure H2 versus H2 seeded in He), and the optical properties of the window used (MgF2 versus CaF2). These different configurations are used to study the VUV irradiation of CO ice at 14 K. In contrast to the majority of studies dedicated to the VUV irradiation of astrophysical ice analogs, which have not taken into consideration the emission spectrum of the MDHL, our results show that the processes induced by photons in CO ice from a broad energy range are different and more complex than the sum of individual processes induced by monochromatic sources spanning the same energy range, as a result of the existence of multistate electronic transitions and discrepancy in absorption cross sections between parent molecules and products in the Ly-α and H2 molecular emission ranges.

VACUUM ULTRAVIOLET AND INFRARED SPECTRA OF CONDENSED METHYL ACETATE ON COLD ASTROCHEMICAL DUST ANALOGS

Following the recent report of the first identification of methyl acetate (CH3COOCH3) in the interstellar medium (ISM), we have carried out vacuum ultraviolet (VUV) and infrared (IR) spectroscopy studies on methyl acetate from 10 K until sublimation in an ultrahigh vacuum chamber simulating astrochemical conditions. We present the first VUV and IR spectra of methyl acetate relevant to ISM conditions. Spectral signatures clearly showed molecular reorientation to have started in the ice by annealing the amorphous ice formed at 10 K. An irreversible phase change from amorphous to crystalline methyl acetate ice was found to occur between 110 K and 120 K.

Vibronic valence and Rydberg transitions in geminal chloro-fluoro-ethene (1,1-C2H2FCl): a spectroscopic and quantum chemical investigation

The vacuum ultraviolet photoabsorption spectrum of 1,1-C2H2FCl has been examined in detail between 5 and 15 eV photon energy by using synchrotron radiation dispersed by three different monochromators. Quantum chemical calculations are performed to help in the analysis of the valence/Rydberg transition region centred at 7.05 eV including the 3a″(π)→π* and the 3a″(π)→3s Rydberg transitions. Interactions between states involving transitions to the 3s, 4d and σ* orbitals are identified. A vibrational analysis is proposed for the structures belonging to these transitions. For the π(3a″)→π* transition, one vibrational progression is observed with ω3 = 1410 ± 50 cm−1 and its lowest excitation energy is determined at about 6.398 ± 0.003 eV. The π(3a″)→3s Rydberg transition is characterised by a single progression with ω3 = 1410 ± 80 cm−1 likely starting at about 6.45 eV. These vibrations are ascribed to the C=C stretching motion. The abundant structure observed in the spectrum between 7.8 and 10.5 eV has been analysed in terms of vibronic transitions to ns (δ = 0.97), np (δ = 0.63 and 0.40) and nd (δ = 0.13 and −0.11) Rydberg states, which belong to series converging to the 1,1-C2H2FCl+() ionic ground state. The analysis of the vibrational structure of the individual Rydberg states has been attempted leading to average values of the wave numbers ω3 = 1420 ± 20 cm−1, ω7 = 720 ± 50 cm−1 and ω9 = 390 ± 50 cm−1. Between 10.5 and 12.5 eV, nine other Rydberg states converging to the 1,1-C2H2FCl+() first excited state were analysed by the same way. The vibrational structure of these Rydberg states results from the excitation of one vibrational normal mode ν7 with an average value of ω7 = 520 ± 20 cm−1, which is assigned to the C–Cl stretching vibration as inferred from quantum chemical calculations.

The KrXe molecule: Modification of potential curves of the ground and first excited electronic states

Potential curves of the ground state of the KrXe molecule and its excited states that converge to the Kr(4p 6 1 S 0) + Xe(5p 56s 3 P 1) atomic states are corrected and tested using the results of modeling published vacuum ultraviolet spectra of a gas-discharge plasma of a krypton/xenon mixture.

Excited states of aniline by photoabsorption spectroscopy in the 30 000–90 000 cm−1 region using synchrotron radiation

The photoabsorption spectrum of aniline (C6H5NH2) in gas phase in the 30,000-90,000 cm(-1) (3.7-11.2 eV) region is recorded at resolution limit of 0.008 eV using synchrotron radiation source for the first time to comprehend the nature of the excited valence and Rydberg states. The first half of the energy interval constitutes the richly structured valence transitions from the ground to excited states up to the first ionization potential (IP) at 8.02 eV. The spectrum in the second half consists of vibrational features up to second IP (9.12 eV) and structureless broad continuum up to the third IP (10.78 eV). The electronic states are assigned mainly to the singlets belonging to π → π* transitions. A few weak initial members of Rydberg states arising from π → 4s, np or nd transitions are also identified. Observed vibrational features are assigned to transitions from the ground state A' to the excited states 1A", 3A', 5A", 6A', and 10A" in C(s) symmetry. Time dependent density functional theory (TDDFT) calculations at B3LYP level of theory are employed to obtain the vertical excitation energies and the symmetries of the excited states in equilibrium configuration. The computed values of the transition energies agree fairly well with the experimental data. Further the calculated oscillator strengths are used to substantiate the assignments of the bands. The work provides a comprehensive picture of the vacuum ultraviolet photoabsorption spectrum of aniline up to its third ionization limit.

Investigation of the Photoionization Properties of Pharmaceutically Relevant Substances by Resonance-Enhanced Multiphoton Ionization Spectroscopy and Single-Photon Ionization Spectroscopy Using Synchrotron Radiation

The photoionization properties of the pharmaceutically relevant substances amantadine, diazepam, dimethyltryptamine, etomidate, ketamine, mescaline, methadone, and propofol were determined. At beamline U125/2-10m-NIM of the BESSY II synchrotron facility (Berlin, Germany) vacuum ultraviolet (VUV) photoionization spectra were recorded in the energy range 7.1 to 11.9 eV (174.6 to 104.2 nm), showing the hitherto unknown ionization energies and fragmentation appearance energies of the compounds under investigation. Furthermore, (1+1)-resonance-enhanced multiphoton ionization (REMPI) spectra of selected compounds (amantadine, diazepam, etomidate, ketamine, and propofol) were recorded by a continuous scan in the energy range between 3.6 and 5.7 eV (345 to 218 nm) using a tunable optical parametric oscillator (spectral resolution: 0.1 nm) laser system. The resulting REMPI wavelength spectra of these compounds are discussed and put into context with already known UV absorption data. Time-of-flight mass spectrometry was used for ion detection in both experiments. Finally, the implications of the obtained physical-chemical results for potential analytical applications are discussed. In this context, fast detection approaches for the considered compounds from breath gas using photoionization mass spectrometry and a rapid pre-concentration step (e.g., needle trap device) are of interest.

Experimental investigation of the shock wave in a fast discharge with cylindrical geometry

The work is devoted to the registration and the study of the properties of cylindrical shock waves generated in the fast discharge (dI/dt ∼ 1012 A/s) inside the ceramic tube (Al2O3) filled by argon at pressures of 100 and 300 Pa. The shock wave appears at the inner wall of the insulator and moves to the discharge axis with a velocity of about (3−4) × 106 cm/s with subsequent cumulation. The plasma behind the front is heated enough to produce radiation in the vacuum ultraviolet (VUV) region, which makes it possible to study its structure by means of a pinhole camera with a microchannel plate detector. The time resolution of the registration system was 10 ns. The analysis of VUV spectra of the plasma shows that the electron temperature behind the shock wave front is about several eV; after the moment of cumulation, its temperature increases to 20–30 eV.

Analysis of vacuum ultraviolet electronic spectra of Ce3+ and Pr3+ ions in Ca9Lu(PO4)7: crystal-field calculations and simulation of optical spectra

The 4f–5d excitation and emission spectra of Ce3+ and Pr3+ ions in Ca9Lu(PO4)7 as recently reported (2012 J. Phys.: Condens. Matter 24 385502) were further analyzed and simulated by employing the effective Hamiltonian model for the 4fN and 4fN−15d electronic configurations of impurity lanthanide ions and the exchange charge model of crystal-field theory. The multi-site effect on the 4f–5d transition spectra was explicitly discussed from the points of view of the local structure and site occupation ratios of lanthanide ions in Ca9Lu(PO4)7. An excellent agreement between the predicted and measured spectra confirms the validity of the performed calculations. Based on these energy level and intensity calculation results, the radiative lifetimes of the 5d–4f emissions of Ce3+ and Pr3+ ions have been modeled to show nearly independent temperature trends. Comparison with the measured lifetimes suggests the nonradiative relaxation process in this host is probably related to the intrinsic defect states. In addition to the studies of the 4f–5d transitions, a general theoretical scheme to calculate the lowest 4f–6s transition energy of the Ce3+ ion was proposed for the first time on the basis of the ligand polarization model. The predicted 6s energy position of the Ce3+ ion in Ca9Lu(PO4)7 is solid evidence corroborating our previous spectroscopic assignment.

Luminescence, cathodoluminescence and Ce3+ → Eu2+ energy transfer and emission enhancement in the Sr5(PO4)3Cl:Ce3+,Eu2+ phosphor

Ultraviolet and vacuum ultraviolet spectra are reported for Ce3+ and Eu2+ singly doped into the Sr-5(PO4)(3)Cl lattice, synthesized by a solid-state process. The maxima of the emission intensities are at 346 nm (Ce3+) and 442 nm (Eu2+), with lifetimes of 25 ns and 494 ns, respectively. The Ce3+ excitation spectra exhibit five bands assigned to vibronic structures of the 4f(1) -> 5d(1) electronic transition, in addition to the host absorption at 166 nm at 295 K. The 5d centroid shift is similar to that in SrCl2:Ce3+. The Eu2+ excitation spectrum is mainly comprised of two 4f(7) -> 4f(6)5d broad bands between 200 nm and 450 nm, peaking at 343 nm and 275 nm. Both of the singly doped systems exhibit concentration quenching, with energy transfer rates being in the low (mu s)(-1) range for concentrations up to 4 at.% of total cations. The energy transfer rates are linearly and quadratically related to dopant ion concentrations of Ce3+ and Eu2+, respectively. The energy transfer between Ce3+ and Eu2+ in the co-doped Sr-5(PO4)(3)Cl lattice has been studied by the analysis of intensity and decay measurements of both Ce3+ and Eu2+ emissions. The electric dipole-electric dipole transfer has an efficiency of 91% in Sr4.8-xCe0.01EuxNa0.01(PO4)(3)Cl, with a critical distance of 21 angstrom. Although energy transfer between Ce3+ and Eu2+ upon excitation into the overlapping Ce3+/Eu2+ absorption band is definitely demonstrated by the dramatic shortening of Ce3+ lifetime, the emission of Eu2+ is also enhanced at low Ce3+ concentrations using exclusive excitation into the Eu2+ absorption band. The quantum yields (QY) of the co-doped system approach those of BaMgAl10O17:Eu2+ (BAM) for the excitation wavelengths of 317 and 365 nm, but are inferior for 254 nm excitation. The addition of 1 at.% Ce3+ to Sr4.98Eu0.02(PO4)(3)Cl increases the QY by similar to 20% of the original value. The cathodoluminesce of the co-doped phosphor is comparable to that of BAM, with CIE coordinates of the emission (0.274, 0.237), so that the application as a field emission display phosphor is proposed.

VUV spectroscopy of formamide ices

Vacuum UltraViolet (VUV) spectra of formamide ice have been studied using synchrotron radiation. VUV spectra of formamide ice recorded at 30K revealed two photoabsorption bands, historically labelled V1 and Q in gas phase VUV spectra. However, in contrast to such gas phase spectra the Q band was found to be more intense than the V1 band in the ice spectra. At higher temperatures changes observed in the spectra have been ascribed to the rearrangement of formamide dimers within the ice. At 160K a phase change from amorphous to crystalline ice was also observed, at higher temperatures (200K) there is some evidence of possible polymerization within the ice.

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.

The vacuum UV photoabsorption spectroscopy of the geminal ethylene difluoride (1,1-C2H2F2). The vibrational structure and its analysis

The vacuum UV photoabsorption spectrum of 1,1-C2H2F2 has been examined in detail between 6eV and 25eV photon energy by using synchrotron radiation. The broad band observed at 7.52eV includes the π→π∗ and the 2b1→3s Rydberg transitions. An analysis is proposed and applied to the fine structure belonging to these transitions. For the π(2b1)→π∗ transition, one long vibrational progression is observed with ω2=1475±80cm−1 combined with one quantum of vibration of ω4=976±24cm−1 and its adiabatic excitation energy is determined at 6.742eV. The 2b1→3s Rydberg transition is characterized by a single progression with ω2=1532±80cm−1 starting at 6.957eV. These vibrations are ascribed to the CC and C–F stretching motions respectively. The abundant structure observed between 8.2eV and 11.2eV has been analyzed in terms of vibronic transitions to ns (δ=0.98) and two different np (δ=0.50 and 0.31) and nd (δ=0.13 and 0.044) Rydberg series all converging to the 1,1-C2H2F2+(X˜2B1) ionic ground state. An analysis of the associated vibrational structure of the individual Rydberg states has been attempted providing average values of the wavenumbers ω2=1549±16cm−1, ω4=839±40cm−1 and ω5=589±16cm−1. Eight other Rydberg states were also analyzed. The vacuum UV spectrum of 1,1-C2H2F2 has been recorded for the first time above 11.2eV and up to 25eV. Several broad and strong bands are tentatively assigned to transitions to Rydberg states which are members of Rydberg series converging to excited ionic states of 1,1-C2H2F2. For several of these Rydberg states vibrational, structures are observed and assignments are proposed.

Visible to vacuum ultraviolet dielectric functions of epitaxial graphene on 3C and 4H SiC polytypes determined by spectroscopic ellipsometry

Spectroscopic ellipsometry measurements in the visible to vacuum-ultraviolet spectra (3.5–9.5 eV) are performed to determine the dielectric function of epitaxial graphene on SiC polytypes, including 4H (C-face and Si-face) and 3C SiC (Si-face). The model dielectric function of graphene is composed of two harmonic oscillators and allows the determination of graphene quality, morphology, and strain. A characteristic van Hove singularity at 4.5 eV is present in the dielectric function of all samples, in agreement with observations on exfoliated as well as chemical vapor deposited graphene in the visible range. Model dielectric function analysis suggests that none of our graphene layers experience a significant degree of strain. Graphene grown on the Si-face of 4H SiC exhibits a dielectric function most similar to theoretical predictions for graphene. The carbon buffer layer common for graphene on Si-faces is found to increase polarizability of graphene in the investigated spectrum.

A compact vacuum UV excilamp on argon dimers

The energy and spectral characteristics of the argon dimer emission with the maximum at a wave-length of ∼126 nm under excitation by a pulse-periodic discharge in a gas flow with pressures higher than the atmospheric pressure are studied. A compact excilamp has been designed for obtaining radiation in the vacuum ultraviolet spectrum region. The minimal argon flow velocities are determined, at which cooling is effected by convective gas ejection from the discharge region. This allows one to form a diffusion discharge with a stable radiation power density. It is shown that, when the flow velocity is 0.5 m3/h, the radiation power density of an Ar2* molecule is >100 μW/cm2 behind a LiF window with ∼10% transmission at a wavelength of 126 nm. It is shown that the use of a windowless design and an increase in the gas flow velocity allows an increase in the radiation power density up to 10 mW/cm2.

The electronic states of 1,2,4-triazoles: A study of 1H- and 1-methyl-1,2,4-triazole by vacuum ultraviolet photoabsorption and ultraviolet photoelectron spectroscopy and a comparison with ab initio configuration interaction computations

The first vacuum ultraviolet absorption spectrum of a 1,2,4-triazole has been obtained and analyzed in detail, with assistance from both an enhanced UV photoelectron spectroscopic study and ab initio multi-reference multi-root configuration interaction procedures. For both 1H- and 1-methyl-1,2,4-triazoles, the first ionization energy bands show complex vibrational structure on the low-energy edges of otherwise unstructured bands. Detailed analysis of these bands confirms the presence of three ionized states. The 6-7 eV VUV spectral region shows an unusual absorption plateau, which is interpreted in terms of the near degeneracy of the first two ionization energies, leading to a pseudo Jahn-Teller effect. The "fingerprint" of the ionization spectrum yields band origins for several Rydberg states. The configuration interaction study shows that although the equilibrium structure for the first cation is effectively planar, the second cation shows significant twisting of the ring system. Some calculated singlet electronic states also show skeletal twisting in which the ring C-H is substantially out of plane.

Structure and dynamics of the electronically excited C 1 and D 0+ states of ArXe from high-resolution vacuum ultraviolet spectra

Vacuum ultraviolet spectra of the C 1 ← X 0(+) and D 0(+) ← X 0(+) band systems of ArXe have been recorded at high resolution. Analysis of the rotational structure of the spectra of several isotopomers, and in the case of Ar(129)Xe and Ar(131)Xe also of the hyperfine structure, has led to the derivation of a complete set of spectroscopic parameters for the C 1 and D 0(+) states. The rovibrational energy level structure of the C 1 state reveals strong homogeneous perturbations with neighboring Ω = 1 electronic states. The analysis of isotopic shifts led to a reassignment of the vibrational structure of the C 1 state. The observation of electronically excited Xe fragments following excitation to the C state rotational levels of f parity indicates that the C state is predissociated by the electronic state of 0(-) symmetry associated with the Ar((1)S(0)) + Xe(6s(')[1/2](0) (o)) dissociation limit. The observed predissociation dynamics differ both qualitatively and quantitatively from the behavior reported in previous investigations. An adiabatic two-state coupling model has been derived which accounts for the irregularities observed in the rovibronic and hyperfine level structure of the C 1 state. The model predicts the existence of a second state of Ω = 1 symmetry, supporting several tunneling/predissociation resonances located ~200 cm(-1) above the C 1 state.

A HIGH-RESOLUTION PHOTOIONIZATION AND PHOTOELECTRON STUDY OF58Ni USING A VACUUM ULTRAVIOLET LASER

In order to provide high-resolution spectroscopic data of nickel (58Ni) and its cation (58Ni+) for the assignment of vacuum ultraviolet (VUV) stellar spectra, we have obtained the photoionization efficiency (PIE) spectra of 58Ni by using a supersonically cooled laser ablation transition-metal beam source and a broadly tunable VUV laser in the range of 61,100-73,600 cm–1, covering the photoionization transitions: Ni+ (3d 9 2 D) ← Ni (3d 84s 2 3 D), Ni+(3d 9 2 D) ← Ni(3d 84s 2 3 F), and Ni+ (3d 84s 4 F) ← Ni(3d 84s 2 3 F). We have also measured the VUV laser pulsed-field-ionization-photoelectron (PFI-PE) spectra of 58Ni in these regions. The VUV-PFI-PE measurement has allowed the determination of a precise value of 61,619.89 ± 0.8 cm–1 (7.6399 ± 0.0001 eV) for the ionization energy (IE) of 58Ni. Due to the narrow VUV laser optical bandwidth of 0.4 cm–1 used in the present study, many complex autoionizing resonances exhibiting Fano line shape profiles are resolved in the PIE spectra. Four autoionizing Rydberg series originating from two-electron and one-electron excitations from the Ni(3d 84s 2 3 F 4) ground state to converge to the respective Ni+(2 D 3/2) and Ni+(4 FJ ) (J = 9/2, 7/2, and 5/2) ion states are identified. The Rydberg analysis, along with VUV-PFI-PE measurements, has yielded highly precise IE values for the formation of these excited ionic states from the Ni(3d 84s 2 3 F 4) ground state. The IE values, relative photoionization cross sections, and autoionizing Rydberg resonances observed in the present study are relevant to astrophysics by enhancing the atomic database of iron group transition metal atoms and for understanding the Ni and Ni+ contribution to the VUV opacity in the solar atmosphere.

Optical, scintillation and thermally stimulated luminescence properties of Sc2Si2O7:Ce single crystal grown by floating zone method

Single crystal of the Sc2Si2O7:Ce (SPS:Ce) was grown by floating zone method. The crystal structure is confirmed to be thortveitite with space group C2/m by X-ray diffraction measurement. The vacuum ultra violet (VUV), photoluminescence excitation (PLE) and photoluminescence (PL) spectra, fluorescence decay time and X-ray excited luminescence spectra were studied. Five sublevels of Ce3+ 5d level are observed through the VUV PLE spectra. The PL is dominated by the fast Ce3+ 5d14f0–5d04f1 transition peaking at 386nm with a single exponential decay of 33ns. The traps in SPS:Ce were also studied through the thermally stimulated luminescence measurement. A trap with level depth 1.16eV with a kinetics order of 1.52 is found in the SPS:Ce crystal.

Kinetic study on pyrolysis of psoralen

In this study, products of psoralen pyrolysis were detected using a solid pyrolysis apparatus and synchrotron radiation vacuum ultraviolet photoionization mass spectrum (SVUV-PIMS). The pyrolytic kinetics of psoralen was also studied by calculating its initial pyrolytic route in quantum chemistry. According to the findings with SVUV-PIMS, three pyrolytic products were observed, CO, C9H6O and C10H6O2. Theoretically, three fragment pathways were calculated for psoralen, in which the major primary decomposition route was de-CO, and the major secondary decomposition reaction was de-CO reaction of de-CO products.