Emission Band System Research Articles

A proposed method for measurement of absolute air fluorescence yield based on high resolution optical emission spectroscopy

In this work, we present a method for absolute measurement of air fluorescence yield based on high resolution optical emission spectroscopy. The absolute measurement of the air fluorescence yield is feasible using the Cherenkov light, emitted by an electron beam simultaneously with the fluorescence light, as a “standard candle”. The separation of these two radiations can be accomplished exploiting the “dark” spectral regions of the emission band systems of the molecular spectrum of nitrogen. In these “dark” regions the net Cherenkov light can be recorded experimentally and be compared with the calculated one. The instrumentation for obtaining the nitrogen molecular spectra in high resolution and the noninvasive method for monitoring the rotational temperature of the emission process are also described. For the experimental evaluation of the molecular spectra analysis we used DC normal glow discharges in air performed in an appropriate spectral lamp considered as an air-fluorescence light emulator. The proposed method and the associated instrumentation could be tested and used in thin or thick target experiments in electron beam accelerators as a candidate optical system for this purpose.

Study of Combustion of Hydrogen—Air and Hydrogen—Methane—Air Mixtures over the Palladium Metal Surface Using a Hyperspectral Sensor and High-Speed Color Filming

The ignition temperature of the 40% H2 + air mixture in the presence of metallic palladium (70°C, 1 atm) was found to be ~200°C lower than above the platinum surface (260°C, 1 atm). In addition, Pd initiated the ignition of (30–60% H2 + 70–40% CH4)stoich + air mixtures at temperatures below 350°C, while Pt foil did not initiate the burning of these mixtures up to 450°C. The effective activation energy of ignition over Pd was evaluated to be ~3.5 kcal/mol. It was found using a hyperspectral sensor that the system of emission bands of H2O* was absent in the range 570–650 nm in the presence of leucosapphire; a possible explanation of this phenomenon was given. An explanation was proposed for the appearance of an additional source of excited water molecules emitting in the range 900–970 nm.

Calculation of Lambda Doubling for 7LiH1 molecule Using the System band emission for electronic transmissions

The A2?u-X1?g+ emission band system of 7LiH1 molecule has been calculated for Lambda doubling. The relation between wave number ?p , ?Q , ?R conducted the energies of the state of rotation F (J), and (J + 1) with rotational quantum number J, respectively, of 7LiH1 molecule for statehood A2?u using the rotation, fixed vibrational states of both the ground and raised crossovers vibrational against ???= 0 to V ' = 0-4using rotational levels J = 0 to J = 20 have found.

Calculation of Lambda Doubling for 7LiH1 molecule Using the System band emission for electronic transmissions

The A2?u-X1?g+ emission band system of 7LiH1 molecule has been calculated for Lambda doubling. The relation between wave number ?p , ?Q , ?R conducted the energies of the state of rotation F (J), and (J + 1) with rotational quantum number J, respectively, of 7LiH1 molecule for statehood A2?u using the rotation, fixed vibrational states of both the ground and raised crossovers vibrational against ???= 0 to V ' = 0-4using rotational levels J = 0 to J = 20 have found.

Low-lying electronic states in bismuth trimer Bi₃ as revealed by laser-induced NIR emission spectroscopy in solid Ne.

Laser-induced near-infrared (NIR) emission spectra of neutral bismuth timer, Bi₃, embedded in solid neon matrixes at 3 K were recorded in a range 870-1670 nm. Using photoexcitation with low energy photons at 1064 nm, two emission band systems were newly identified by their origin bands at T₀ = 6600 and 8470 cm⁻¹. Accordingly, spectral assignment for three NIR emission band systems reported recently was partly revised for the one with its origin band at T₀ = 7755 cm⁻¹ and reconfirmed for the others at T₀ = 9625 and 11,395 cm⁻¹. Energy splitting by spin-orbit coupling between the pair of electronic energy levels in the ground state of bismuth trimer, Bi₃, both having a totally symmetric vibrational mode of frequency at ω(e)" = 150 cm⁻¹, was determined to be 1870 ± 1.5 cm⁻¹. Transitions from the pair of electronically excited states, locating at T₀ = 8470 and 9625 cm⁻¹ above the ground state and separated by spin–orbit coupling of 1155 cm⁻¹, have relatively long decay constants of τ ∼0.2 and ∼0.1 ms, respectively.

Improved direct potential fit analyses for the ground electronic states of the hydrogen halides: HF/DF/TF, HCl/DCl/TCl, HBr/DBr/TBr and HI/DI/TI

The potential energy and Born–Oppenheimer breakdown functions for the X1Σ+ ground electronic states of the hydrogen halides HF, HCl, HBr, and HI are reported in full analytic form. All available pure rotational and vibrational–rotational spectroscopic data for the various isotopologues of the four HX molecules, as well as the B1Σ+→X1Σ+ emission band system data for HF/DF and HCl/DCl, were employed in direct potential fit determinations of the various radial functions. Significant improvements over previous work have been made to the mathematical models for these functions, particularly with respect to the behavior of the potential energy in the long-range region where dispersion forces between the component atoms dominate. The MLR3 model for the potential energy is employed, allowing for constraint of the three leading dispersion coefficients C6, C8, and C10, for the X states of HF and HCl. Quantum-mechanical rotational and centrifugal distortion constants are calculated for all isotopologues considered in the non-linear least-squares fitting procedures. Computer code is provided in order that precise calculation of all functions for all isotopologues is possible for a user-specified radial grid. Precise estimates are obtained for X state equilibrium internuclear separations for the principal isotopologues of all four halides, namely re(HF)=0.91683897±0.00000004Å, re(H35Cl)=1.27454677±0.00000006Å, re(H79Br)=1.4144292±0.0000001Å, and re(HI)=1.6290588±0.0000004Å.

Observation of new near infrared emission band systems of small bismuth clusters in solid neon matrix

Laser induced fluorescence (LIF) spectroscopy was applied to small bismuth clusters embedded in a solid neon matrix at 3 K. Near infrared (NIR) optical emission spectra were recorded in a range of 6200–11 600 cm-1 by an excitation with 1.79 eV photons using a pulsed dye laser system. Three new NIR band systems were identified by their origin bands at 8207, 9625 and 11 395 cm-1. Each of the NIR systems exhibited the vibrational progression with a common lower state frequency at 151 cm-1. Temporal decay profiles for selected NIR emission bands showed upper state lifetimes on the order of a hundred of microseconds, explainable by the transition between mixed spin states. Low-lying electronic states for small bismuth clusters, Bi n (n = 2 − 4), are discussed along the theory and experiment reported so far.

Novel molecular discharge light sources

A systematic investigation into transition metal halides and oxides showed the high potential of transition metal oxides as visible radiators for highly efficient gas discharge light sources. Zirconium monoxide (ZrO) has been identified as the most promising candidate combining highly attractive green and red emission band systems with very high dissociation energy (8.2 eV) which ensures that the molecule is stable even at the hot plasma centre. Thus far, however, it has been impossible to keep ZrO in the gas phase of a closed discharge vessel, because at wall temperature usually compounds are formed which have negligible vapour pressures. We succeeded in establishing a regenerative chemical cycle by filling ZrX4 (X = Cl, Br, I) together with a stable, but volatile oxygen compound (like MoO2X2) and realized thus highly attractive, novel gas discharge light sources.

Discovery of the FeO orange bands in the terrestrial night airglow spectrum obtained with OSIRIS on the Odin spacecraft

An unidentified pseudo‐continuum in the 600 nm region is observed in the upper mesosphere with the limb‐scanning OSIRIS imaging spectrograph on‐board the Odin spacecraft. Averages of low latitude spectra at a series of tangent limb altitudes from 75 to 105 km are assembled and matched with synthetic spectra of the known night airglow emission band systems to isolate the underlying airglow continuum. The upper limit of the NO + O → NO2* air afterglow continuum component in the observed 600 nm pseudo‐continuum is estimated to be 5% at low latitudes. The spectral profile of the unidentified 600 nm residual airglow continuum is very similar to published laboratory measurements of the ‘orange bands’ of FeO. The volume emission rate altitude profile of this 600 nm airglow continuum, derived from averaged limb radiance profiles, is very similar in shape and in altitude to the concurrently observed Na vertical profile suggesting related source mechanisms.

Electronic Spectroscopy of UO2Cl2 Isolated in Solid Ar

Laser-induced fluorescence spectra have been recorded for uranyl chloride isolated in a solid Ar matrix. Pulsed excitation was examined using a XeCl excimer laser (308 nm) and a dye laser operating in the 19 500−27 500 cm−1 range. Several absorption and emission band systems were observed. The emission spectra were characterized by a nearly harmonic vibrational progression with a frequency of 840 cm−1 starting at 20 323 cm−1. The electronic absorption spectra were dominated by five harmonic vibrational progressions with frequencies of approximately 710 cm−1. Comparisons with theoretical calculations indicate that all of the transitions observed were associated with the UO2+2 subunit. They involved the promotion of an electron from a bonding orbital to the metal-centered 5fδ and 5fϕ orbitals. Band origins and vibrational constants for five excited states were obtained. Fluorescence was observed from the lowest-energy excited state alone, regardless of the excitation wavelength. The decay curve was found to be biexponential, with characteristic decay lifetimes of 50 and 260 μs.

Calculation of radiative transition probabilities and radiative recombination rate coefficients for H2, OH, H 2 + and OH+ molecules

A method is presented to calculate the radiative transition probabilities and the radiative recombination rate coefficients between electronic molecular states. Total transition probabilities are determined from vibrational transition probabilities without considering the detailed rotational structure of the molecular electronic states. Radiative recombination rate coefficients are obtained from the computation of vibrational photo-ionisation cross sections. Concerning spontaneous emission, Lyman (B → X) and Werner (C → X) band systems of H2 and Meinel (A → X), (B → A) and (B → X) band systems of OH are investigated. For radiative recombination, transitions between H 2 + (X) and H2(X), and between OH+(X, a, A, b, and c) and OH(X) are considered. Transition probabilities and recombination rate coefficients are calculated as a function of temperature in the range 1500–15 000 K.

Ultra low frequencies phenomena in Jovian decametric radio emission

System of periodic peaks is found in the power spectra of ULF flux oscillations of Jovian decametric emission, which is observed at fixed frequencies. This result could be interpreted in terms of an ionospheric Alfven resonator near Jupiter. Standing Alfven wave could explain the system of emission bands in the dynamic spectrum of decametric emission. The space period of such bands and the frequency of standing waves have been used to estimate electron number density in the low magnetosphere of Jupiter. The result is consistent with radio occultation data. Hence, the ULF modulation hypothesis appears validated.

The B Σ+ and X 1Σ+ Electronic States of Hydrogen Fluoride: A Direct Potential Fit Analysis

All literature pure rotational and vibration-rotational spectroscopic data on the ground X (1)Sigma(+) electronic state of HF and DF, together with the entire set of spectroscopic line positions from analyses of the B (1)Sigma(+) --> X (1)Sigma(+) emission band systems of HF and DF, have been used in a global least-squares fit to the radial Hamiltonian operators, in compact analytic form, for both electronic states. With a data set consisting of 6157 spectroscopic line positions, the reduced standard deviation of the fit was sigma = 1.028. Sets of quantum mechanically significant rotational and centrifugal distortion constants were calculated for both electronic states using Rayleigh-Schrödinger perturbation theory.

A dispersed fluorescence and ab initio investigation of the X̃B12 and ÃA12 electronic states of the PH2 molecule

In this work, the X̃B12 and ÃA12 electronic states of the phosphino (PH2) free radical have been studied by dispersed fluorescence and ab initio methods. PH2 molecules were produced in a molecular free-jet apparatus by laser vaporizing a silicon rod in the presence of phosphine (PH3) gas diluted in helium. The laser-induced fluorescence, from the excited ÃA12 electronic state down to the ground electronic state, was dispersed and analyzed. Ten (υ1υ2υ3) vibrationally excited levels of the ground electronic state, with υ1⩽2, υ2⩽6, and υ3=0, have been observed. Ab initio potential-energy surfaces for the X̃B12 and ÃA12 electronic states have been calculated at 210 points. These two states correlate with a Πu2 state at linearity and they interact by the Renner-Teller coupling and spin-orbit coupling. Using the ab initio potential-energy surfaces with our RENNER computer program system, the vibronic structure and relative intensities of the ÃA12→X̃B12 emission band system have been calculated in order to corroborate the experimental assignments.

Inter- and intramolecular excited state proton transfer in 2-hydroxy-9H-carzole-1-carboxylic acid

Absorption, fluorescence and fluorescence excitation spectroscopy and single photon counting time dependence spectrofluorimetry have been used to study the inter- and intramolecular excited state proton transfer (ESIPT) reactions in 2-hydroxy-9H-carbazole-1-carboxylic acid (2-HCA). Except in cyclohexane and water (pH 5) dual fluorescence is observed in rest of the solvents used. Normal Stokes shifted band seems to originate from 2-HCA-1-c and tautomer emission band from the tautomer formed by ESIPT in 2-HCA-1-c followed by structural reorganization. Both these emission band systems originate from the same ground state species. AM1 and CNDO/S-CI calculations have been carried out to establish the identity of the species. Different prototropic equilibria have been determined and discussed.

Nature of the emission band of Dergaon meteorite in the region 5700x2013;6700 Å

An emission band system in the region 5700–6700 A from Dergaon stoney iron meteorite which fell at Dergaon, India on March 2, 16.40 local time (2001) was excited with the help of a continuous 500 mW Ar+ laser. The band system is attributed to silicate (olivine), a major component of the meteorite.

The optimum characteristics of a halogen lamp pumped by transverse RF discharge

We report on the optimized characteristics of a small-size bactericidal lamp pumped by transverse RF (f=1.76 MHz) discharge, operating on a system of the molecular emission bands of chlorine in a wavelength range of 195–310 nm. The spectral characteristics of the plasma emission were measured and the intensity of chlorine emission bands were studied as functions of the total pressure and partial composition of a helium-chlorine mixture. Oscillograms of the pumping current and output radiation intensity were measured and the total output radiation power was determined. It is established that the lamp radiates predominantly in a bactericidal wavelength interval on an electron-vibrational transition at 200 nm in Cl2** molecules. The optimum partial pressures of helium and chlorine are 100–300 and 90–120 Pa, respectively. The maximum output power of UV emission from the side cylindrical surface of the lamp reached 10 W. The lamp can be used in photochemistry, ecology, genetics, and medicine.

Spectroscopic study of the 24Mg35Cl and 24Mg37Cl A²pi-X²sigma+ band system

The A2P-X2S+ emission band system of the MgCl molecule has been studied by means of high resolution Fourier Transform Spectroscopy (FTS). The MgCl species were produced by mixing Mg vapor with a gaseous flow of a He/Cl2 and excited in a ''heated'' Schuller's type discharge tube. Rovibrational analysis of the 0-0 and 0-1 bands was performed and the values of the vibrational constant we of the ground state and the spin-orbit constants A0 and AJ of the A2P state were determined. For the first time transitions of the isotopic species 24Mg37Cl could be assigned and included in the analysis presented here.

Supercritical argon as a mobile phase for the flame photometric detection of sulfur

The background emission properties of supercritical argon and supercritical carbon dioxide mobile phases in packed column supercritical fluid chromatography (pSFC) with flame photometric detection (FPD) were compared. As column flow rates were increased toward common values used in pSFC, the carbon dioxide background emission grew enormously. The resulting emission spectrum displayed dominant features at wavelengths between 325 and 525 nm, consisting of a complex series of overlapping molecular emission band systems partly attributed to CO* and CH*. By comparison, when using the same flow rates with a supercritical argon mobile phase, the background emission was identical to that of the FPD flame without column effluent. In terms of intensity, when using a column flow rate of 2 mL/min, supercritical carbon dioxide contributes a background emission in the FPD that is about 3 × 105 times larger than that produced by supercritical argon. This difference leads to an improvement of two orders of magnitude in the pSFC-FPD signal-to-noise ratio for sulfur when a supercritical argon mobile phase is used. Results indicate that supercritical argon could also be advantageous for the pSFC-FPD analysis of other elements.Key words: supercritical fluid chromatography, packed column, flame photometric detection, supercritical argon.

Ultraviolet and visible dispersed spectroscopy for the photofragments produced from H2O in the extreme ultraviolet

The photofragmentation of H2O has been studied by fluorescence spectroscopy at photon energies between Ehν=16.9–54.5 eV. The primary photon beam was monochromatized undulator radiation supplied from the UVSOR synchrotron radiation facility. The fluorescence in the wavelength range of 280–720 nm was dispersed with an imaging spectrograph. The dispersed spectra exhibit the hydrogen Balmer lines of H*[n2LJ′′→2 2LJ″″(n=3–9)] and the emission band systems of H2O+[Ã 2A1(0,v2′,0)→X̃ 2B1(0,0,0)], OH+(Ã 3ΠΩ,v′→X̃ 3Σ−,v″), and OH(Ã 2Σ+,v′→X̃ 2ΠΩ,v″). The fluorescence cross sections for these transitions have characteristic dependences on Ehν and vibrational quantum numbers. The cross section summed over the Balmer lines takes a minimum value at Ehν=21.7 eV and is very small even at 24.9 eV beyond which it steadily increases with increasing Ehν. This behavior is understood as that the superexcited states correlating with H*(n⩾3)+OH(Ã 2Σ+) are too repulsive to be accessible below Ehν∼30 eV by the Franck–Condon transitions from H2O(X̃ 1A1) and as that the Balmer emission below 30 eV is mainly due to the H*(n⩾3)+H(n=1)+O(3Pg) channel. The appearance energy of the OH+(Ã 3ΠΩ,v′→X̃ 3Σ−,v″) transitions is found to be ca. 25.5±0.3 eV. This value is much higher than the dissociation limit of 21.5 eV for the OH+(Ã 3ΠΩ)+H(n=1) channel, but is consistent with the vertical ionization energy to H2O+[(1b1)−2(4a1)1 2A1] that has been assumed to correlate with the above dissociation limit in the literature. The vibrational distribution of OH+(Ã 3ΠΩ) evaluated from the OH+(Ã 3ΠΩ,v′→X̃ 3Σ−,v″) band intensities is similar to the prior distribution in the rigid-rotor harmonic-oscillator approximation.