VUV Fluorescence Research Articles

VUV fluorescence following electron-impact dissociative excitation of CS2

Electron-impact dissociation of CS${}_{2}$ has been studied by observation of the atomic spectral emission features in the range 115--170 nm. Absolute photoemission cross sections are presented over the complete wavelength range for an incident electron energy of 100 eV. As an example, the measured cross section of the strong C i emission at 165.7 nm, which is a prominent feature in many solar and other extraterrestrial spectra, is ($1.45\ifmmode\pm\else\textpm\fi{}0.19)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}$ cm${}^{2}$. Comparison with earlier cross-sectional measurements suggest that these were too high by a factor of more than three. Excitation functions of the dominant C i (156.1 nm) and S i (147.4 nm) emission lines have been measured for electron-impact energies from threshold to 360 eV. From appearance energy measurements in the near-threshold region, likely fragmentation channels are identified which involve both two-fragment breakup and total fragmentation of the parent CS${}_{2}$.

Double photoionization of N2 into the N22+ D 1Σu+-state

Double photoionization of N2into the N22+D1Σu+-stateas a function of the exciting-photon energy has been investigated experimentally andtheoretically. Photon-induced fluorescence spectroscopy using monochromatizedsynchrotron radiation in the exciting-photon energy range between 50 and 66.5 eVand recording of the intensity of the dispersed VUV fluorescence between 145 and167 nm has been carried out. Relative cross sections as a function of theexciting-photon energy have been determined. The experimental results arecompared with ab initio calculations.

Dissociative single and double photoionization with excitation between 37 and 69 eV in N2

Dissociative single and double photoionization of N2 as a function of the exciting-photon energy has been investigated using monochromatized synchrotron radiation in the exciting-photon energy range between 37 and 69 eV by dispersed VUV fluorescence spectroscopy (80 nmfl200 nm). Relative partial emission cross sections for N I and N II fluorescence have been recorded as a function of the exciting-photon energy. There is strong evidence that the precursors of dissociative single ionization with one of the fragments being excited are the N2+ 2g-1 2g+ state with its closely lying correlation states only. An approximately linear excess energy dependence of the cross sections for the molecular double photoionization into the N22+ D 1u+ state has been observed in the excitation spectrum of D 1u+ X 1g+ fluorescence in N22+ close to its threshold. Evidence for dissociative double photoionization with excitation has been found.

State resolved detection of Cl, Br, CIO and BrO

Nascent CIO and BrO products in photodissociation or reaction processes were observed in a state resolved manner by applying the two-photon laser-induced fluorescence technique, where two simultaneously absorbed laser photons excite the products to the C-state. CI and Br atoms can be observed by means of three-photon excitation with subsequent recording of the VUV fluorescence light. The advantage of this detection technique, other than the simpler laser system, is the use of low energy photons which don't interfere with other processes. State resolved detection of BrO products has been performed in the reactions 0(1D)+CF3Br and Br+03.The photodissociation of OCl0(2A2v1,v2,v3)→Cl0(X2πω, v,J,λ)+0(3P) in the 356–371 nm region is clearly a function of the initial type of motion of OC10(2A2vl,v2,v3). The population of the fragment rotational levels is observed to resemble Boltzmann distributions of around 1000 K. When high vibrationally excited states of the symmetric stretch mode of OC10(2A2v1>17,v2,v3) are excited, then most of the available energy is transferred to CIO vibration. Those extremely vibrationally excited CIO products carry sufficient energy to react with ambient nitrogen in the atmosphere, which is confirmed in a final end product analysis where the formation of N20 is observed.The Cl quantum yield of the minor OCIO(2A2 v1,v2,v3) → CI(2PJ) + 02 channel depends on the state of the parent molecule and is of the order of 4%.

A time resolved VUV fluorescence study of hydrogen clusters: evidence of a liquid phase

Abstract The mobility of Xe atoms captured from a cross jet by hydrogen clusters is investigated with time resolved VUV fluorescence excitation spectroscopy. A band blue shifted by 0.5 eV with respect to the 5p→6s transition of free Xe atoms is observed. It is attributed to Xe atoms profoundly embedded in hydrogen clusters and surrounded by several layers of hydrogen. The complete absence of features related to surface sites gives evidence that after the pick up process the xenon atoms penetrate deep into the interior of the hydrogen clusters. This indicates that hydrogen clusters show a liquid-like behavior similar to helium clusters, though their estimated temperature (∼6 K) is much below the triple point of hydrogen (14 K).

Alignment of Xe II and Xe III ionic states after the decay of the Xe I 46p P autoionization resonance

The angular dependence of the UV/VIS and VUV fluorescence was measured to determine the alignment of Xe II and Xe III ionic states populated via the decay of the Xe I autoionization resonance through (multi-step) spectator-Auger or Auger-shake transitions. The anisotropy of the fluorescence radiation and the alignment parameter were also determined for a decay cascade involving electron as well as fluorescence transitions starting from the Xe I resonance and ending in the Xe II ground state .

Stepwise multiphoton excitation of the 4f 25d configuration in Nd 3+: YLF

Stepwise multiphoton excitation of the 4f 25d configuration of Nd 3+: YLF via intermediate levels in the 4f 3 configuration is investigated with nanosecond laser pulses. Strong UV and VUV fluorescence from the 4f 25d configuration is observed as a result of three-photon absorption of 532 nm laser pulses from a frequency doubled Nd: YAG laser. Excitation spectra from 520–536 nm show that the efficiency of the three-photon excitation of the 4f 25d configuration is maximized at 521 nm and 526 nm.

Neutral dissociation of N 2O in superexcited states

Neutral dissociation of a superexcited N 2O molecule has been studied by measuring dispersed vuv fluorescence spectra of dissociation fragments as a function of the excitation wavelength. Obtained spectra are presented as a two dimensional fluorescence excitation spectrum (2D-FES). The 2D-FES clearly shows the complex neutral dissociation behavior of superexcited states of N 2O.

Studies of fluorescence from photoexcitation of N 2 and CO 2 in the 28–100 eV region

Fluorescence excitation functions produced through photoexcitation of N 2 and CO 2 using synchrotron radiation in the range 28–100 eV have been studied. Two broadband detectors were employed to simultaneously monitor fluorescence in the 1080–3000 Å and 3000–7000 Å regions, respectively. Broad fluorescence peaks are observed and are interpreted in terms of dissociative ionization excitation of multiple electronic states, ion states and Rydberg states converging to multiply charged N 2 and CO 2 (i.e., N 2 m+ and CO 2 m+ for m=1−3). We have also studied the temperature effect on the relative fluorescence yield of CO 2 in the 28–60 eV region. It was found that the VUV fluorescence yields in the 28–40 eV region increase as sample temperature increases from 295 K to 650 K suggesting that the fluorescence produced by photon excitation of CO 2 hot bands may be important.

Threshold behaviour of neutral photodissociation with excitation of CO probed by dispersed fragment VUV fluorescence

Dispersed VUV fluorescence emitted from photodissociation fragments in the wavelength range between 90 and 200 nm has been recorded following the neutral photodissociation of CO using monochromatized synchrotron radiation for exciting-photon energies close to the respective dissociation thresholds. Qualitatively different energy dependencies of the fluorescence intensities have been observed close to the thresholds. Atomic carbon fluorescence at wavelengths of 119, 128, 132.9, and 146 nm has been observed for the first time after neutral photodissociation with excitation of CO.

Synchrotron radiation induced photoionization and photodissociation of carbon monoxide in the 14?35 eV region

Carbon monoxide has been excited with monochromatic synchrotron radiation in the 14–35 eV range using the Swedish synchrotron facility MAX in Lund. The decay products were studied in various detection channels such as formed CO+ and C+ ions using mass spectroscopy and visible or VUV fluorescence using photon detection. A rich line structure is observed which is attributed to CO Rydberg series converging to theX,A,B,D,C andE states in CO+. While a great number of these lines are already known, some of them are classified here for the first time. The combination of information from the fluorescence spectra and the mass spectra contribute important information concerning the autoionization and predissociation of these various Rydberg series.

VUV and UV fluorescence and absorption studies of Pr^3+-doped LiLuF_4 single crystals

The laser-induced fluorescence spectrum of LiLuF(4):Pr(3+) single crystals, pumped by an F(2) pulsed-discharge molecular laser at 157 nm, was obtained in the VUV and UV regions of the spectrum at room temperature. A number of new fluorescence peaks were observed for the first time to our knowledge. They were assigned to the dipole-allowed transitions 4f5d ? 4f(2) of Pr(3+) ion. In addition, the absorption spectrum of the crystal samples was recorded. The positions of the bands with the 4f5d configuration were found to be 46 412, 53 267, and 63 397 cm(-1) from the ground state, (3)H(4), of the Pr(3+) ion. The edge (onset) of the 4f5d bands was at 45 100 cm(-1).

Visible and VUV fluorescence from synchrotron radiation induced photoionization and photodissociation of molecular oxygen

Photon induced fluorescence from O2 has been studied in various emission regions 1150-6500 Å in the excitation range 14-28eV using the Swedish synchrotron facility MAX in Lund. A rich line structure is observed which is interpreted in terms of autoionization and dissociation of Rydberg levels converging to the a, b, c, and B states in O2+. New features have been observed, for instance, concerning the (c 4Σu−) 3sσg Fano resonance which has been viewed in detail in different detection channels including O2+ and O+ ions.

Discharge‐flow/chemiluminescence and flash‐photolysis/resonance fluorescence studies of the reaction O + SiH4 at room temperature

AbstractDF‐CL studies using NO2 chemiluminescence detection of O yielded a rate constant k1 for O + SiH4 of (2.6 ± 0.5)×10−13 cm3 s−1 at 295 K, where the 95% confidence interval reflects accuracy. FP‐RF studies using flash photolysis of SO2 followed by time‐resolved vuv fluorescence detection of O at 295 K yielded k1 = (3.0 ± 0.5) ×10−13 cm3 s−1. These results are in good accord with most previous measurements and lead to a combined best estimate of k1 = (3.2 ± 0.4) × 10−13 cm3 s−1. The DF‐CL and FP‐RF methods appear to have little unrecognized systematic error. © 1993 John Wiley & Sons, Inc.

On the interconfigurational 4f25d−4f3 VUV and UV fluorescence features of Nd3+ in LiYF4 (YLF) single crystals under F2 laser pumping

Abstract Fluorescence spectra and kinetics of LiYF4(YLF):Nd3+ single crystals pumped by an F2 pulsed discharge molecular laser at 157 nm have been obtained in the VUV and UV regions of the spectrum between 150–300 nm. With this pumping scheme some new fluorescence peaks have been observed. The high photochemical stability of this material under the above pumping scheme suggests that it can be used as an active medium for VUV tunable laser sources. ft]1|Permanent address: Kazan State University, 18 Lenin Str., 420008 Kazan, Russian Federation.

Radiative lifetimes and collisional deactivation of two-photon excited xenon in argon and xenon

Radiative lifetimes and bimolecular rates have been determined for two-photon laser excited states of Xe* (5p56p, 5p56p′, 5p57p) in argon and xenon buffer gases. The collisional deactivation rates are found to be very large for the Xe 6p′ and 7p states [∼(2–5)×10−10 cm3/s] while the rates for the Xe 6p states are comparatively smaller [∼(0.06–1.2)×10−10 cm3/s]. In general, the quenching rates in argon are about a factor of 2 smaller than the xenon quenching rates for the same excited state with the notable exception of Xe 6p[1/2]0. For Xe 6p[1/2]0, a multicomponent decay has been observed in argon buffer gases. The second component is attributed to collisional coupling to Xe 5d[1/2]1 which lies 132.3 cm−1 below Xe 6p[1/2]0. Quench rates determined from the collisionally induced VUV fluorescence from Xe 5d[1/2]1 at 125 nm are in excellent agreement with this assignment. Furthermore, these experiments have unambiguously identified the product channel involved in the curve crossings observed in studies of optical collisions [N. Böwering, T. D. Raymond, and J. W. Keto, Phys. Rev. Lett. 52, 1880 (1984)].

VUV and uv fluorescence lifetimes of Cl 2

A spectroscopic study of Cl 2 by VUV laser-induced fluorescence is reported for the first time. The free jet excitation spectrum in the region between 79000 and 80100 cm −1 revealed the contribution of some additional band systems other than the dominant 2 1Σ u +←X 1Σ g + transition system. The VUV and UV fluorescence lifetimes ranging from 15 ns down to 1 ns or less depended strongly upon the excitation wavelengths, but very little on the fluorescence wavelengths. Possible assignments of the excitation bands are discussed.

Quantitative VUV spectroscopy of Cl2

The photoabsorption and fluorescence cross sections of Cl2 were measured in the 105–145 nm region using synchrotron radiation as a light source. The oscillator strengths for the major absorption bands were calculated from the measured absorption cross sections. The measured oscillator strengths for the 2 3Πu and 2 1Πu←X 1Σ+g transitions agree quite well with the theoretical values. The absorption spectrum was analyzed in accord with the excited electronic states calculated by Peyerimhoff and Buenker (1981). The Rydberg series converging to the first and second ionization potentials were classified. The vibrational levels of the 2 1Σ+u ionic state were determined up to v′=15 from the fluorescence excitation spectrum. It was observed that a band with peak at 108.3 nm produces VUV fluorescence, but it produces UV fluorescence only by a collisional excitation process.

A high efficiency spectrometer for VUV fluorescence radiation

A VUV fluorescence spectrometer for very low photon rates has been developed which incorporates a position-sensitive microchannel plate with extended long wavelength (up to 180 nm) sensitivity for multiplex detection of VUV fluorescence spectra after selective excitation by monochromatized synchrotron radiation. The system has worked well at count rates as low as 0.1 photons −1 nm −1. The performance of the system was demonstrated by first observations of VUV fluorescence continua of H 2 molecules in the B and C electronic states which have been rotationally selectively excited out of the molecular ground state.

Competition between photodissociation and photoionization in methyl iodide

CH 3I has a number of 5pπ → 6p Rydberg states which can be excited by two-photon absorption from the ground state. These two-photon absorptions have been previously detected by molecular ionization with a third photon. They can also be studied by observation of the VUV fluorescence from neutral photofragments (excited iodine atoms) following absorption of a third photon. Similarly it is found that absorption of one photon at 118 nm (10.5 eV) is followed by dissociation into excited iodine atoms as well as ionization. Iodine atom VUV emission is 2–10 times stronger from CD 3I than from CH 3I.