Emission Band System Research Articles

High-Resolution Fourier Transform Study of MgCl: The A2Π–X2Σ+ Band System

The A2Π–X2Σ+ emission band system of the MgCl molecule has been studied by means of high-resolution Fourier transform spectroscopy. Excited MgCl molecules were produced by two different techniques: (i) at Orsay, they were created by mixing Mg vapor with a flow of He/Cl2 and excited in a “heated” Schüller-type discharge tube, and (ii) at Waterloo, they were generated by using a copper hollow cathode lamp loaded with MgCl2 powder. Rovibronic analysis of the (0, 0) and (0, 1) bands was performed. Molecular constants were derived in a weighted nonlinear least squares fit, including both the new line positions and the previously published microwave frequencies (M. Bogey, C. Demuynck, and J. L. Destombes, Chem. Phys. Lett.155, 265 (1989); Y. Ohshima and Y. Endo, Chem. Phys. Lett.213, 95 (1993)).

UV and Visible Emission Spectra from the Photodissociation of Carbonyl Sulfide Using Synchrotron Radiation at 15–30 eV

Abstract The photofragmentation of OCS at photon energies of 15–30 eV has been studied by dispersed fluorescence spectroscopy. The primary photon beam was monochromatized undulator radiation supplied from the UVSOR facility. The following emission-band systems have been identified: OCS+[A2ΠΩ(0,0,0) → X2ΠΩ(0,0,v3′′)], CO+(A2ΠΩ → X2Σ+), CS+(B2Σ+ → A2ΠΩ), and CO(d3Δ → a3Π). All of the transitions, except for OCS+[A2ΠΩ → X2ΠΩ], were first observed in the vacuum UV photodissociation of OCS. The fluorescence excitation spectra for the OCS+[A2ΠΩ(0,0,0) → X2ΠΩ(0,0,v3′′)] and CS+(B2Σ+ → A2ΠΩ) transitions were measured in the photon energy range of 15.1–15.75 and 21.8–26 eV, respectively. The emission spectra obtained at 20.85 and 22.9 eV exhibit atomic transitions of S[nd3Do → 4p3Pe (n = 6–9)], which result from the neutral dissociation of superexcited Rydberg states of OCS into S(nd3Do) + CO. Possible excited states of the counterpart CO are discussed on the basis of the difference in the n distribution between the two spectra.

Refined potential-energy surfaces for the 2A" and à 2A' electronic states of the HO2 molecule

In a previous paper (G. Osmann et al. J. Mol. Spectrosc. 197, 262 (1999)) we calculated ab initio the potential-energy surfaces of the ground [Formula: see text]2A" and excited Ã2A' electronic states of the HO2 molecule; these two states correlate with a 2Π state at linearity and participate in a Renner effect interaction. In that paper, we also calculated the electric- and magnetic-dipole moment and transition-moment surfaces, and the spin-orbit coupling constant; we then simulated the à ® [Formula: see text] emission band system including both electric-dipole and magnetic-dipole transitions. We now calculate more points on the surfaces to cover a wider range of bending geometries, and then refine the surfaces by fitting to rovibronic term values for both electronic states simultaneously. In the fitting we include levels having J values up to 9/2 and term values up to about 8000 cm–1. In our calculation of the energy levels we allow for the Renner effect and spin-orbit coupling by using our variational computer program RENNER. A good fitting to the data is obtained and as a result we obtain an accurate representation of these two potential surfaces over an energy range of more than 1 eV. We tabulate the vibronic energies up to 1 eV for both HO2 and DO2. We can explain the origin of a perturbation observed in the F1 spin component levels of the Ã(0, 0, 0) vibronic state for J values around 51/2; this is caused by a spin-orbit interaction satisfying Δ N = ± 1 with the F2 spin component levels of the [Formula: see text](1,1,2) vibronic state. Using the new rovibronic energies and wave functions, with our ab initio electric dipole moment and transition moment surfaces, we calculate Stark coefficients and compare them with experiment for some ground vibronic state levels. PACS Nos.: 31.20D, 31.50, 33.10, 33.20E, 35.20D, 35.20J

The optical spectrum of HCSi

A new emission band system has been observed in the gas phase at around 850 nm. This system correlates with absorption bands previously measured in a neon matrix and assigned to a triplet electronic transition of SiC. However, the gas phase bands display a clear doublet structure. Preliminary molecular parameters resulting from the rotational analysis of the (000) - (000) band coincide with the expected values obtained by a recently published ab initio calculation carried out on the HCSi radical. We conclude that both the gas phase and the neon matrix spectra originate from the HCSi radical which is here identified for the first time.

Tables of vacuum ultraviolet emission band systems of molecular nitrogen from 82.6 to 124.2 nm

Observed wavenumbers of the emission lines belonging to 10 vacuum ultraviolet band systems of molec- ular nitrogen are classied into 283 bands, 220 of them reported for the rst time 1 .

Controlled formation of state selected SiO metastables using a new pyrolysis source

Abstract A controlled and readily reproducible thermolysis of silane (SiH 4 ) entrained in both an argon and helium carrier is used to form the precursor whose oxidation prepares long-lived yet readily monitored SiO b 3 Π metastables in high yeild. A simple yet novel pyrolysis-N 2 O oxidation source produces the b 3 Π metastables, yet no evidence is obtained for the formation of the lower-lying SiO a 3 Σ + state. This result, which is in sharp contrast to observations made when an oven generated, helium or argon entrained silicon beam is oxidized with N 2 O, suggests either an unusual symmetry constraint and selective reaction branching to the b 3 Π state or the highly efficient quenching of the a 3 Σ + state. This implies that a surprisingly similar quenching of the a 3 Σ + state must occur in distinctly different helium or argon diluted silane based environments. An analysis of the observed SiO A 1 Π- X 1 Σ + and b 3 Π- X 1 Σ + emission band systems produced with the silane based source demonstrates that the SiO b 3 Π state is formed apparently selectively in a ratio exceeding 2200 times that of the remaining SiO excited states. The results obtained with the present pyrolysis N 2 O source are contrasted to the continuous chemiluminescent emissions associated with thermalized silane-ozone and silane-oxygen reaction environments.v The current means of generating SiO metastables would appear to (1) allow the creation of a long path length medium for the efficient energy transfer pumping of visible chemical laser amplifiers and oscillators and (2) form the basis of a useful method for the control and efficient monitoring of SiO surface deposition processes.

Optical emission spectra of Ag3 molecules in the gas evaporation technique

A study was conducted of optical emission spectra, taken at a region near the source of the evaporation of Ag in a low pressure helium gas (100 Torr). A new Ag3 emission band system was identified. Spectroscopic constants for an excited and a lower state (the ground state) in the gas phase were derived as follows: ν00=19 809.4±2.0 cm−1, ω′1=106.8±1.0 cm−1, x′11=−0.2±0.5 cm−1, ω″1=129.0±1.0 cm−1, and x″11=−0.1±0.5 cm−1 for the 107Ag2109Ag trimers. Spectroscopic constants for three other isotope species were also derived. The lower state was the 2B2 ground state.

Emission and Relaxation of Electronically Excited O2 Doped in a Low Temperature N2 Crystal

Oxygen molecules doped in a low temperature N2 crystal were irradiated at 240‐260 nm. Two emission band systems were observed, one from the v′ = 0 level of A′ 3Δu state to X3Σg-. state and the other, from the v′ = 0 level of c1Σu-. state to at a1Δg state, independent on the excitation wave length. The latter emission grew together with the decay of the former emission at around the same rate after the pulsed laser excitation, which implies that the vibrational levels of c state lying below the v′ = 0 level of Ω = 3 of A′ state are populated from the v′ = level of A′ state, though some additional mechanism for populating the c state may exist. The rate was found to become larger with the increase of the crystal temperature. It was also found that the excitation spectrum obtained by monitoring the A′–X emission was the same as that obtained by the c–a emission. The progress of vibrational relaxation, coupling with the intersystem crossing between the Herzberg states, will be discussed.

High-resolution spectroscopy with a CCD array detector: application to the 2880 Å emission band system in I2

The 2880 Å system in the Tesla discharge spectrum of I2 in Ar is reexamined using a CCD array detector to record spectra for both 127I2 and 129I2. This charge-transfer transition terminates on a weakly bound valence state, giving a highly congested spectrum with fine violet-degraded band structure barely perceivable on a pseudocontinuous background. The superior signal-to-noise capabilities of the array detector permit a great improvement in the precision and number of measured bandheads, as compared with previous results obtained from photographically recorded spectra. The new data span a larger range of vibrational levels in the lower state and lead to a change in the previous ν″ numbering by −3 units. Both states can now be located precisely on the absolute energy axis through least-squares fits in which the lower state energy is represented as a near-dissociation expansion. The primary spectroscopic constants (cm−1) are [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] The lower state has a dissociation energy of 287.5 cm−1 and supports 35 bound levels, subject, however, to possible further revision due to a remaining uncertainty of 1 unit in the ν″ numbering. The previous tentative electronic assignment of this system remains in effect: The upper state is likely the [Formula: see text] state that correlates with I−(1S) + I+(3P1), while the lower state is the [Formula: see text] component of the lowest valence 3Πu multiplet.

A review of the O2 ( a1Δg) and O2 ( b1Σg+) airglow emissions

The state of knowledge of the Infrared Atmospheric and the Atmospheric emission band systems of molecular oxygen is reviewed. These emissions are present in the nightglow, the twilight, and the dayglow. The available observations are collected in a data base model with the capability of displaying and manipulating the data in a number of ways. The observational data base is used to examine the state of theoretical understanding of the atmospheric photochemistry of these emissions. These emissions are of interest to future space experiments — in particular the WINDII and IIRDI experiments on the Upper Atmospheric Research Satellite — which will use them to measure state parameters of the middle atmosphere such as temperature and wind velocity. While the IR Atmospheric system in the dayglow is both well characterized observationally and well understood theoretically, the other emissions are neither, suggesting an immediate need for additional work in this area to support UARS.

Anomalous intense ultraviolet emission bands in the radio-frequency glow discharges of GeH4-fluorocarbon-H2 mixtures

Anomalous intense ultraviolet emission bands in the region 320–370 nm with a maximum at 340 nm were observed in radio frequency glow discharges of CF4-H2 mixtures containing 0.3%–1% of GeH4. The system of emission bands is prominent also in the discharges of GeH4-C2F6-H2 mixtures but the corresponding emission system was not observed in the discharge spectra of GeH4-CH4-H2 and SiH4-CF4-H2 mixtures. From the vibrational analysis of the bands, it was found that the emission bands almost agree with the weak emission system of GeF2, which has been tentatively assigned in earlier work as the 3B1–1A1 transition.

On the BiF bond dissociation energy and an evaluation of the BiF red emission band systems

The chemiluminescent emission from the Bi + F 2 and Bi 2 + F reactions has been characterized. A study of the chemiluminescent reaction of argon entrained bismuth vapor and molecular fluorine over a substantial pressure range (60–333 Pa) provides evidence for two distinct electronic transitions of BiF in the region 565–740 nm, at least one of which is thought to terminate in the BiF “1” (X 21) state arising from the 3Σ − (σ 2π 4π *2) configuration of BiF. The observed transitions with ν 00 ≈ 17631 cm −1 and ν 00 ≈ 15244 or 15784 cm −1 exhibit pronounced upper state vibrational relaxation and are characterized, especially at the highest pressures, by a dominance of progressions eminating in ν′ = 0 and terminating in several ν″ lower state levels. The higher energy transition with ν 00 ≈ 17631 cm −1 is believed to terminate in the recently observed BiF “1” state with ν 00 ≈ 6768 cm −1 (X 2 1-X 1O +). The upper state, denoted A′, with T 0 ≈ 24400 cm −1 is believed also to be a “1” state based on limited high resolution data for at least two bands of the system. The correlation made here is in close accord with recent quantum chemical calculations which suggest that the “1” state lies ≈ 7200 cm −1 above ν″ =0, XO +. The levels of the A′ upper state appear to correlate precisely with several BO + perturber state levels. This perturber state, thought to lie less than 2000 cm −1 above the AO + (II) state may play an important role with respect to energy disposal among the excited states of the BiF molecule. The second transition with ν 00 ≈ 15244 or 15784 cm −1 also appears to terminate in the “1” state suggesting a second upper state, denoted A″, lying at 22552 ± 545 cm −1 virtually isoergic with AO + (II). Alternatively, the second transition might eminate from the ν′ = O upper state level at T 0 ≈ 24400 cm −1 terminating in a lower state with T 0 ≈ 8615 cm −1. In order to establish the dissociation energy of the BiF molecule and to determine whether this controversial bond is closer to 3 or 5 eV, both the (Bi, Bi 2) + F 2 and (Bi, Bi 2) + F 2 reactive systems have been studied. Combined results based on the observation of the chemiluminescent Bi + F 2 and Bi 2 + F reactive encounters producing BiF AO + (II)-XO + and BO +-XO + emission features suggest that the BiF bond energy is closer to 5 eV.

HgI(B2Σ+1/2) formation by electron impact dissociative excitation of HgI2 molecules: applications to the HgI laser

Electron impact dissociative excitation of HgI2 molecules producing the B2 Sigma +1/2 state of HgI has been studied in the case of low energy electrons. Using the most intense band of the (B2 Sigma +1/2-X2 Sigma +1/2) system of the HgI radical at 444 nm, emission cross sections have been measured in the electron energy range 1-100 eV. The threshold electron energy for the observation of the (B2 Sigma +1/2-X2 Sigma +1/2) emission band system has been determined to be 5.7 eV. The role of such dissociative excitation in lasing was analysed.

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A new weak emission band system of the SeO molecule consisting of 34 band heads degraded to shorter wavelengths has been observed for the first time in the spectral region 6730–8570 Å. The vibrational analysis of the system suggests that it arises from the transition A3Πreg-X0+, 1. All the five subsystems allowed by the selection rule ΔΩ = 0, ±1 have been identified. The constants in cm−1 derived for the A3Π state are (Here the Te values are expressed with respect to the minimum in the Ω = 0+ component of the ground electronic state X. The Te value of the A33Π2 component is estimated by using the vibrational constants of the components A1 and A2 since ΔG(12) is practically the same for all three components.) An approximate value of the rotational constant B0 of state A estimated from the separations of the observed P and Q heads and the known rotational constant of state X is = 0.470 cm−1 (for 3Π0).

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A new weak emission band system of the SeO molecule consisting of 34 band heads degraded to shorter wavelengths has been observed for the first time in the spectral region 6730–8570 Å. The vibrational analysis of the system suggests that it arises from the transition A3Πreg-X0+, 1. All the five subsystems allowed by the selection rule ΔΩ = 0, ±1 have been identified. The constants in cm−1 derived for the A3Π state are (Here the Te values are expressed with respect to the minimum in the Ω = 0+ component of the ground electronic state X. The Te value of the A33Π2 component is estimated by using the vibrational constants of the components A1 and A2 since ΔG(12) is practically the same for all three components.) An approximate value of the rotational constant B0 of state A estimated from the separations of the observed P and Q heads and the known rotational constant of state X is = 0.470 cm−1 (for 3Π0).

Collisional studies involving metastable species (N2(A) and HgBr2/CH3HgBr collisions)

A novel technique to improve the efficiency of mercury bromide lasers is described. N2(A-X), N2(B-A), and N2(C-B) emission band systems are observed besides atomic lines of sodium when a microwave discharge is passed through a flowing vapour of NaN3 in a quartz tube. The HgBr (B-X) band system and atomic mercury lines also are detected during collisions of N2(A) both with HgBr2 and CH3HgBr. In collisions involving CH3HgBr and N2(A), the CH(A-X) and CN(B-X) emission band systems are found as well. From the integrated intensity of the most intense band (0, 22) at 502nm of the HgBr (B-X) transition, the ratio of the rate of formation of HgBr (B-state) during collisions of HgBr2 and CH3HgBr with N2(A) has been determined to be 2·3:1.

Discharge emissions from NaN 3 related to the HgBr laser

N 2( A-X), N 2( B-A) and N 2( C-B) emission band systems and atomic lines of sodium have been observed by passing a microwave discharge through flowing vapors of NaN 3 in a temperature range of 200–280°C. Emission of the HgBr( B-X) band system and atomic lines of mercury has been observed during collisions involving HgBr 2 + N 2(A) as well as CH 3HgBr + N 2( A). For CH 3HgBr + N 2( A) collisions, emission bands of CH and CN radicals have also been observed. On the basis of the intensity of the (0,22) band of the HgBr( B-X) transition, the efficiency ratio of HgBr( B-state) formation due to HgBr 2 + N 2( A) with respect to CH 3HgBr + N 2( A) collisions, has been determined to be 2.3:1.

The ultraviolet spectrum of DF: Rotational analysis of the B1Σ+-X1Σ+ emission band system

The B1Σ+-X1Σ+ emission band system of deuterium fluoride has been recorded with a 10.7-m spectrograph in the wavelength range 205–275 nm. Computer assisted rotational analyses of 41 bands with 0 ≤ v′ ≤ 5 and 16 ≤ v″ ≤ 26 have resulted in precise band origins and rotational parameters for both electronic states. Vibronic term values relative to the energy of v″ = 16 have been obtained through correlated least-squares fitting of the band orgins. The dissociation energy of the ground state has been estimated as De = 49420 ± 35 cm−1 by considering rotational predissociation in the higher vibrational levels. The electronic isotope shift from HF has been determined as ΔTe = −23 ± 5 cm−1. Franck-Condon factors for several values of the rotational quantum number have been generated on the basis of Rydberg-Klein-Rees potentials calculated for both electronic states.

Rotational analysis of the A2Π → X2Π system of As35Cl+

Abstract The visible A2Π → X2Π emission band system of AsCl+ has been recorded photoelectrically at medium resolution in the wavelength range 5210–7215 A. Twelve 2Π 1 2 2Π 1 2 sub-bands of As35Cl+ with ν′=0,1 and 14≤ν″≤25 have been rotationally analysed. A total of 425 line positions have been employed in direct least-squares fits of the molecular parameters of the two states. The equilibrium internuclear separations are re(X) = 2.031 and re(A) = 2.498 A.

Electronic excitation of HgX (X = Cl, Br, I) due to electron and methyl mercury halide collisions

Electronic excitation of Hg X ( X = Cl, Br, I) radicals in the B-state has been observed as the result of collisions with low energy electrons and methyl mercury halide (CH 3Hg X) molecules. The emission intensity has been observed to be much weaker than that observed for electron-Hg X 2 collisions under similar experimental conditions. Using the strongest band head of the B-X band system, an attempt has been made to calculate the emission cross section due to electron CH 3Hg X collisions at 10 eV electron kinetic energy. For HgCl, HgBr, and HgI radicals, these cross sections are 1 × 10 -18, 7 × 10 -17, and 2 × 10 -17 cm 2, respectively, with an estimated uncertainty of ±30%. Our measured threshold electron energy for excitation of CH 3Hg X molecules and observation of the B-X emission band system and emission cross sections measured at 10 eV are greatly different from those measured by Allision and Zare [ Chem. Phys. 35, 263 (1978)].