Afterglow Spectra Research Articles

The Vacuum Ultraviolet Absorption Bands of the Pink Afterglow Spectrum of Molecular Nitrogen Revisited at High Resolution

The absorption spectrum of the pink afterglow of molecular nitrogen in the vacuum ultraviolet has been analyzed at high resolution. The spectrum exhibits hot bands involving vibrational levels of the electronic ground state as high asv" = 19. Experimentally determined term values are derived forv" = 0–19, of whichv" = 16–19 were before now poorly known.

Identifying the Environment and Redshift of Gamma‐Ray Burst Afterglows from the Time Dependence of Their Absorption Spectra

The discovery of gamma-ray burst (GRB) afterglows revealed a new class of variable sources at optical and radio wavelengths. At present, the environment and precise redshift of the detected afterglows are still unknown. We show that if a GRB source resides in a compact (100 pc) gas-rich environment, the afterglow spectrum will show time-dependent absorption features due to the gradual ionization of the surrounding medium by the afterglow radiation. Detection of this time dependence can be used to constrain the size and density of the surrounding gaseous system. For example, the Mg II absorption line detected in GRB 970508 should have weakened considerably during the first month if the absorption occurred in a gas cloud of size 100 pc around the source. The time-dependent H I or metal absorption features provide a precise determination of the GRB redshift.

A Search for Optical Afterglow from GRB 970828

We report on the results of R-band observations of the error box of the gamma -ray burst of 1997 August 28 made between 4 hr and 8 days after this burst occurred. No counterpart was found varying by more than 0.2 mag down to R=23.8 . We discuss the consequences of this nondetection for relativistic blast wave models of gamma -ray bursts and the possible effect of redshift on the relation between optical absorption and the low-energy cutoff in the X-ray afterglow spectrum.

Electronic Trap Defects in Y2O3:Eu and (Y,Gd)2O3:Eu X-Ray Scintillators

ABSTRACTDetailed properties of the defects and energy transfers responsible for afterglow in transparent sintered ceramic Y2O3:Eu and (Y,Gd)2O3:Eu based scintillators have been determined by transient thermoluminescence ('TL) and spectral measurements of afterglow emission. X-ray excited TTL spectra between 150 K and 350 K reveal 4 defect transitions for 3 mole percent Eu. Adequate modeling of this data requires for each defect transition a trap depth energy, an attempt-to-escape frequency, a broadened density of trap state energies, and a trap filling frequency. These defect parameters have been determined and can be used to predict afterglow dependence on time after excitation shut-off, exposure time, and temperature. The afterglow emission spectra at all temperatures are characteristic of Eu under S6 site-selective UV excitation of these rare-earth C-type structure scintillators. This indicates that states associated with the Eu activator on the S6 site are the terminal states upon thermal release of trapped charge carriers.

New perspectives on the Venus nightglow

We have reanalyzed the 190‐ to 250‐nm nightglow spectrum of Venus recorded by the Pioneer Venus Orbiter. This spectrum is known to consist primarily of v′ = 0 features of the NO δ‐ and γ‐bands. However, the summed spectra, taken over many orbits, have weak and previously unidentified bands in the same spectral region, which we interpret as originating from higher vibrational levels of NO(A2Σ+), resulting from collisional relaxation of NO(C2Π)v = 0. The intensity of the airglow is quite variable, with the average number of photon counts in a spectral scan being 3, while the maximum counts observed is 65. We divided the scans into a high‐count group and a low‐count group. The resulting partial‐sum spectra and the wide intensity variations suggest that at least two sources of excitation are operating. The low‐count spectrum looks similar to an N + O afterglow spectrum taken at relatively high pressure, containing a variety of relaxed NO states, and thus appears to have been generated at low altitude. The high‐count spectrum is unrelaxed, and resembles a photoexcitation spectrum of the C2Π (v = 0) state, and thus would reflect N + O recombination at higher altitudes. Of particular interest is a set of three consecutive intense spectra taken on the same orbit, which suggests the presence of a long (1000 km), straight, and narrow (∼5 km) track of secondary NO excitation, possibly caused by a meteor.

The Effect of Neon and Argon Additions on Improving Selectivities in the Helium Afterglow Discharge Detector

The ultraviolet (UV) spectra of the helium (He) afterglow and mixed gas helium-neon (He-Ne) and helium-argon (He-Ar) afterglows are presented. The effect of Ne and Ar on the He afterglow background spectrum and on the selectivities (versus carbon) for sulfur and phosphorus detection in the UV region is discussed.

Cathodically and Anodically Biased Electroluminescence Decays at Aluminum‐Manganese Alloys

The electroluminescence (EL) decay of Al‐Mn alloys is investigated in sulfuric acid solution. The afterglow spectrum and brightness decay are obtained from cathodically and anodically biased experiments. The influence of the anodic oxide thickness, amplitude, and frequency of the square voltage, and temperature are studied. The brightness decay from both types of experiments fits a first‐order law, although the light intensity from the cathodically biased runs is about ten times greater than that resulting from the anodically biased runs. The explanation of these results is given in terms of the following physical mechanism. The activator is excited by an injected charge trapped in a metastable state. The slow afterglow decay observed in the EL spectra results from a recombination of charge carriers. The latter process is practically independent of the direction of the applied electric field but the corresponding intensity depends on the charge carrier concentration available for the recombination process. Hence, the intensity of the cathodically biased EL decay as it involves electron injection and no faradaic process is much greater than the anodically biased EL decay which involves hole injection and a faradaic reaction. The latter acts as a quenching reaction for those charge carriers.

The rotationally-resolved oxygen afterglow, 373–474 nm

Microdensitometer traces of the oxygen-argon afterglow spectrum obtained by Degen et al. (1968, Identification Atlas of Molecular Spectra, 6. The O 2 A 3 Σ u +− X 3 Σ g − Herzberg I system. York University, Toronto, Canada) are presented. They show rotationally-resolved bands of the A 3 Σ u +− X 3 Σ g −, A′ 3 Δ u − a 1 Δ g , and c 1 Σ u −− X 3 Σ g − systems, in the 373–474 nm region. Relative populations of and O( 1S) in O 2, He/O 2, and Ar/O 2 afterglows are discussed.

The study of afterglow spectra of nitrogen at different temperatures and pressures

The afterglow spectra of nitrogen in the range from 1900 to 8000 A were studied at 77 K and 300 K using a sophisticated equipment having some new characteristic features. The relative vibrational intensities for the first positive system have been computed from the afterglow spectra at both temperatures. The pressure dependence of intensities of various bands have been investigated at pressures between 2 and 7 Torr while the effect of a diluent like argon has been studied at a fixed argon pressure of 5 Torr and a nitrogen pressure varying from 0.2 to 3 Torr. The mechanisms for populating the different vibrational levels of the B 3Πg state are dicussed in the light of the new results obtained in the present experiment and previous measurements reported in the literature.

Rotational and vibrational analysis of the O2(A′ 3Δu → a 1Δg) system

The oxygen afterglow spectrum published by Degen in 1968 has been reanalyzed. It is found to contain three O2(A′ 3Δu → a 1Δg) bands and four O2(A 3Σu+ → X 3Σg−) bands, and by computer simulation, rotational and vibrational constants have been determined for particular levels of the A′ 3Δu(Ω=3) and a 1Δg states.

Site Effects on N and O Luminescence in Electron‐Irradiated Neon Films

AbstractThe visible luminescence spectrum of solid neon containing small amounts of N2 or O2 is investigated at 7.8 K using low‐energy electrons. Double‐doping experiments employing N2 and × (where × is either O2, CO or Ar) are also carried out. Particular attention is given to the interpretation of the α(N2D—4S) transition of matrix‐trapped N atoms, and to a lesser extent the β(O1S—1D) transition of matrix‐isolated O atoms. The spectral intensity distribution within these transitions is photoelectrically recorded and for the long lived α transition, afterglow spectra are also presented. The structure of the α transition is shown to depend upon both the ratio of the N2 and × concentrations as well as the total [N2 + X] concentration, for total guest concentrations in the range from 0.01% to 0.1%. The components which comprise this emission arise from N atoms trapped in two characteristic sites denoted “substitutional”‐ and “impurity”‐affected. This same interpretation also applies in large part to the β transition of trapped O atoms.

Afterglow of zeolite crystals activated by tin atoms Snº

The afterglow spectra of zeolite monocrystals (30 to 40 μm in size) activated by tin atoms Sno are measured at T = 300 and 80 K. Investigations of the afterglow decay kinetics prove that such decay is determined by an intracenter process, the exitation level lifetime being equal to about τ ≈ 20 μs. The band in afterglow spectrum is identified with the forbidden emission transition 3P00 - 1D2 in Sn0-centres, the possible mechanisms of manifestation of which are discussed here. [Russian Text Ignored.]

Rotational analysis of the B3Π(0+) → X1Σ+ band systems of 35Cl35Cl and 35Cl37Cl in the chlorine afterglow emission spectrum

The B3Π(0+) → X1Σ+ band system of Cl2, excited by the recombination of ground state Cl2P32 atoms at total pressures near 2 Torr, has been rotationally analyzed in the range 6300–9900 Å. About 30 bands, with 0 ≤ v′ ≤ 6 and 5 ≤ v″ ≤ 14, were investigated, mostly for both 35Cl35Cl and 35Cl37Cl. The band origins and rotational constants for the B state were obtained with the help of the known constants for the ground state. The principal molecular constants (cm−1) for the B3Π(0+) state of 35Cl35Cl are as follows: Te′ = 17 817.67(3); ωe′ = 255.38(3); ωe′xe′ = 4.59(1); ωe′ye′ = −0.038(8); De′ = 3341.17(14); Be′ = 0.16313(3); αe′ = 2.42(3) × 10−3; γe′ = −5.7(7) × 10−5. The equilibrium internuclear separation is 2.4311(2) Å. The results of Briggs and Norrish on a transient absorption spectrum of Cl2 assigned as 0g+ ← B3Π(0+) are reinterpreted with the present constants.

Spectroscopic studies of the sulphur afterglow

The afterglow emission spectrum of sulphur and argon mixture is found to consist of (a) the main band system of S 2( B 3 Σ - u − X 3 Σ - g ) in the region 3200–6600 Å and (b) the atomic spectrum of argon in the 7500–9000 Å region. Although B− X bands of S 2 obtained by ordinary excitation extends from 2829 to 7100 Å, the lower wavelength limit of these bands from the afterglow is only 3200Å. It is proposed that the S 2 molecules are formed in the B 3Σ - u state through inverse predissociation when two S atoms approach each other along the potential curve of the predissociating electronic state 1 u.

Recombination of ground state halogen atoms. Part 2.—Kinetics of the overall recombination of chlorine atoms

The kinetics of overall recombination of 2P ground-state chlorine atoms have been investigated by internsity measurements on the chlorine afterglow emission spectrum Cl2(3IIou+→1Σ+g). For Cl2 or Ar as third body at total pressures near 2 torr, no evidence supporting a major recombination path via Cl3 as an intermediate was found. The mechanism of homogeneous recombination could be represented by the simple reaction [graphic omitted] with k3,M=½[M]–1 d([Cl]–1)/dt. Measurements of k3,Ar from 195 to 500°K gave k3,C;2= 1015.1 exp(+1600 ± 600 )RT= 1016.3(T/300)[–2.7 ± 0.5] cm6 mole–2 sec–1 and k3, Ar= 1014.3 exp (+ 1800 ± 700/RT)= 1015.6(T/300)[–3.0 ± 0.5] cm6 mole–2 sec–1. Methods for the determination of rate constants for chlorine atom reactions in discharge-flow systems are discussed.

Kinetic of the chlorine afterglow emission spectrum

Kinetic studies of the chlorine afterglow spectrum, Cl 2 3Π ou+ → 1Σ + g) in a discharge-flow system showed dependences of intensity distribution upon both [Cl] and total pressure. The mechanism probably involves depopulation of Cl 2( 3Π ou+) by a radiationless transition involving Cl ( 2P 3 2 ).

Spectral Emission of the Helium Afterglow

The spectral emission from a dc pulsed helium discharge for pressures from 5 to 30 Torr has been investigated during the early afterglow using a spectrometer with gated photomultiplier and from the early afterglow through the late afterglow using interference filters with gated photomultiplier. The afterglow spectrum was predominately that of molecular light which was attributed to the collisional-radiative recombination of molecular ions. The time-decay of molecular light at late times indicated ambipolar diffusion control by an ion with a Dap of 710±10 cm2/sec, which corresponds to a μ0 of 16.4±0.2 cm2/V·sec, in good agreement with values reported for the helium molecular ion employing other techniques.

Absorption et postluminescence de CS 2

A new carbon disulphide afterglow spectrum is being investigated by photography. This emission spectrum extends from 6000 Å to 3500 Å. It is located on the long wavelength side of the near ultraviolet absorption spectrum (3980 Å-2770 Å). It is being shown that the ground level is not common to the two systems, contrary to what occurs in the case of the sulphur dioxide molecule. The final level of the transition corresponding to the afterglow emission is excited. Near the red limit, the absorption spectrum shows a peculiar increase of the absorption coefficient when the temperature is increased from 300°K to 900°K. This effect is not due to the formation of a new chemical species, but simply to the increase of the population of high vibrational levels of the normal molecule, in quantitative agreement with a Boltzmann distribution. The potential energy function of the unstable initial level corresponding to the recombination between a normal sulphur atom and a normal carbon monosulphide molecule has been calculated approximately. The binding energy of this molecule corresponds to that of inert gas Van der Waals type molecules.

Spectra of afterglows and discharges from nitrogen-oxygen mixtures

A systematic investigation has been made of the spectra of the afterglows resulting from electric discharges in mixtures of nitrogen and oxygen. The spectra have been photographed for mixtures ranging from 100% nitrogen to 100% oxygen, pressures from 1 to 5 mm Hg, flow rates from 2 to 20 cm 3/sec, and as a function of time after the discharge. The spectrum range covered is from 3000 to 11,000 A, making use of both a prism spectrograph ( f 4 ) and a grating spectrograph ( f 0.8 ). Curves have been prepared to show the relative variations of the individual spectral features as function of the various parameters.

A New Method for the Production of Active Nitrogen and its Application to the Study of Collision Effects in the Nitrogen Molecular Spectrum

The source described employs a high tension arc and can operate at comparatively high pressures. The afterglow spectrum is that of the Lewis-Rayleigh glow at low pressures, but is modified at the higher pressures. Reasons are given for interpreting this modification as due to exchanges of vibrational energy occurring in collisions between nitrogen molecules. A modification is made to Mitra's theory of active nitrogen.