Measured collisional radiative coefficients of the 4p groups of the argon I and argon II systems

We determine the r¹ (p) coefficients of the argon I 4p ¹P₁ state (2p₂ with Paschen notation) with the λ = 696.5 nm line and of the argon II 4p ²D_{$\text{5}\text{2}$} state with the λ = 488.0 nm line in a highly ionized, low temperature (T_{e = 3?4 eV}), magnetically confined (0.2 T) plasma of a hollow cathode arc with electron densities n_e between 10¹⁹ and 10²⁰ m^?3. The neutral density n₀ is 10¹⁹ m^?3 or less. The r¹ (4p) values are (6 ± 2) × 10^?5 for argon I and (5 ± 2) × 10^?4 for argon II.     

Measurement of Ar(I) and Ar(II) transition probabilities in LTE ARC plasmas

The transition probabilities of two Ar(I) lines and one Ar(II) line have been measured in emission on wall-stabilized argon arc plasmas (0·5×10⁵?p, Nm^-2?3×10⁵; 10,000?T, K?20,000; 10²²?N_e, m^-3?5×10²³) using the “method of best fit (MBF)”. The results (without line-wing correction) are for Ar(I) at 714·7 nm, A_nm=5·66×10⁵ s^-1±5%; for Ar(I) at 430·0 nm, A_nm=3·40×10⁵ s^-1±5%; for Ar(II) at 480·6 nm, A_nm=8·82×10⁷ s^-1±7%. These values were not influenced by deviations from LTE, which have been observed at electron number densities n_e?10²³ m^-3. The small uncertainties were achieved after careful corrections of different sources of error.     

Intensities and half-widths at different temperatures for the 201III←000 band of CO2 at 4854 cm−1

Measurements made at temperatures of 197, 233, and 294°K of the absolute intensities and self-broadening coefficients for the vibration-rotation lines of the 201_III←000 band of the ¹²C¹⁶O₂ molecule, are reported. From these measurements, values have been derived for the vibration-rotation interaction factor (F_VR), the purely vibrational transition moment (|R(O)|), and the intensity (S_Band). The results are: E_VR(m) = 1+(2.2±0.7)×10^?3m+(5.6±1.6)×10^×5m², |R(0)| = (2.064±0.017)×10^?3 debye, S_Band = 21,329±69 cm^?1km^?1atm^?1_STP. The results for the self-broadening coefficients are presented in the text.     

Measurement at different temperatures of absolute intensities,line half-widths,and broadening by Ar and N2 for the 3001II←0000 band of CO2

Absolute intensities, self-broadening coefficients, and foreign-gas broadening by Ar and N₂ were measured at temperatures of 197, 233 and 294 K for the 30⁰1_II←00⁰0 band of CO₂ at 6348 cm^-1. Also, the intensity parameters and total band intensity were calculated. We obtained for the vibration-rotation interaction factor the value F(m) = 1 + (0.26 ± 0.06) × 10^-2m + (0.92 ±0.32 × 10^-4 m²; for the purely vibrational transition moment, we found ¦R₀₀₀₀^3001_II¦к(0.4351 ± 0.0014)()10^b3 debye; and, for the total band intensity at STP conditions, S_band(30⁰1_II←00⁰0)_STP = 1255 ± 9 cm^-1 km^-1 atm^-1.Self-broadening coefficients at 197 and 294 K were also measured, as well as broadening by Ar and N₂. Foreign-gas-broadening efficiencies (Ar and N₂) were determined. Finally, a comparison is made with measurements by other authors and with theoretically calculated values.     

Resonance Raman and fluorescence spectra of chlorine dioxide in argon,krypton, xenon,and nitrogen matrices at 16 K

Laser excitation studies of matrix-isolated ClO₂ at 16 K using the 4579, 4765, 4880, and 5145 Å argon ion lines and argon, krypton, xenon, and nitrogen matrices were conducted. Quenching of fluorescence by the matrix was evidenced by the observation of displaced bands in the Ar, Kr, and N₂ work and increased background in the Xe studies. An intense progression in ν₁ of ClO₂ with regularly decreasing intensities out to 6ν₁ observed in solid Ar with 4579 Å excitation was attributed to the resonance Raman effect. Shorter resonance Raman progressions were observed in Xe and N₂ matrices.     

On some geometrical consequences of physical symmetries

It is shown that there exists only one submanifold O^(4,m)₂ of the representation space C^4m of the group GL(4,C)×GL(m,C) which admits a unique projection onto Minkowski space, consistent with the group. We describe the decomposition of this manifold O^4,m)₂ when the group is restricted to the physical symmetry group SU (2,2)× ×SU(m) or P×SU(m). We consider also representations of SU(2,2)×SU(m) in the resulting submanifolds and in the Hilbert space of functions over these manifolds.     

Der Einfluß metastabiler Atome auf den statischen Durchschlag in Argon

A gas discharge in argon is initiated by an ultraviolet light pulse which releases 10⁵ electrons at the cathode within 20 nsec. The time of built-up for the static breakdown is found to be in the order of msec. The oscillogram of the current near breakdown shows a fast component consisting of several successive avalanches caused by secondary electrons liberated by ions at the cathode and a slow component which is due to the electrons liberated by metastable atoms at the cathode. The second Townsend coefficient for argon ions and a nickel cathode is determined to beγ ₊= 2.5·10^?3. The amount of electrons liberated by metastables at static breakdown is 25% of the total number of secondary electrons. The mean life-time of the metastables at 1,1 Torr and an electrode separation of 10 mm is found to be 2.2 msec, which is mainly due to de-exciting collisions at the electrodes.     

Elektronennachlieferung in Niederdruckentladungen durch metastabile Stickstoffmoleküle und deren Stoßlöschung durch Fremdgase

Oscilloscopic studies of pre-breakdown discharge currents in pure nitrogen and mixtures of nitrogen with other gases show that metastable N₂ molecules influence the discharge by releasing secondary electrons when they collide with the electrodes. By this slow process an after current is produced, which lasts a time of milliseconds. It was found that the diffusion coefficient of the metastable N₂ molecule is 167 cm² s^?1 ±15% at 1 Torr and 20°C, its radiative life time is larger than 40 ms, and its cross section for deexciting collisions with ground state N₂ molecules is smaller than 7 · 10^?22 cm². There is strong evidence that the metastables are in theA ³Σ _u ⁺ state. From measurements in gas mixtures cross sections for deexciting collisions with other molecules are derived. The results are for O₂ 1.9 · 10^?17 cm², for CO 1.5 · 10^?17 cm², for H₂ 2.5 · 10^?20 cm², and for CO₂ smaller than 5 · 10^?20 cm².     

Experimental evidence for the complete saturation phase in the argon neutral system

An experimental study of the population densities of excited states confirms the existence of the complete excitation saturation phase in the argon neutral system. Collisional radiative coefficients r⁽¹⁾_m are independent of n_e and decrease with decreasing ionization energy. At higher n_e-values the levels are observed to come consecutively into Saha equilibrium (PLTE).     

Tunable diode laser measurements of spectral parameters of HCN at room temperature

A tunable infrared diode laser was used to record 17 fully resolved vibration-rotation transitions in the v₁ fundamental band of HCN at 3μ. The experiments were conducted in an absorption cell on room temperature mixtures of HCN diluted by N₂ and Ar. The v₁ fundamental band strength of HCN was determined to be 267±8 cm^-2 atm^-1 at 273.2 K. Small but significant reductions in the residual errors were obtained by using the Galatry profile rather than the Voigt profile to fit the experimentally recorded line shapes. Collisional broadening and narrowing parameters were determined simultaneously from Galatry profile fits to the data. The collision-broadened linewidths of HCN lines in N₂ and Ar were determined as a function of rotational quantum number of transitions ranging from P(14) to R(14) (3268.22-3353.29 cm^-1). The optical diffusion coefficients of HCN in N₂ and Ar at 300 K were determined from the collisional narrowing parameters and were 0.074±0.01 and 0.016±0.03 cm²s^-1 respectively.     

Investigation of the kinetics of OH∗ and CH∗ chemiluminescence in hydrocarbon oxidation behind reflected shock waves

The temporal variation of chemiluminescence emission from OH^?(A² Σ ⁺) and CH^?(A² Δ) in reacting Ar-diluted H₂/O₂/CH₄, C₂H₂/O₂ and C₂H₂/N₂O mixtures was studied in a shock tube for a wide temperature range at atmospheric pressures and various equivalence ratios. Time-resolved emission measurements were used to evaluate the relative importance of different reaction pathways. The main formation channel for OH^? in hydrocarbon combustion was studied with CH₄ as benchmark fuel. Three reaction pathways leading to CH^? were studied with C₂H₂ as fuel. Based on well-validated ground-state chemistry models from literature, sub-mechanisms for OH^? and CH^? were developed. For the main OH^?-forming reaction CH+O₂=OH^?+CO, a rate coefficient of k ₂=(8.0±2.6)×10¹⁰ cm³?mol^?1?s^?1 was determined. For CH^? formation, best agreement was achieved when incorporating reactions C₂+OH=CH^?+CO (k ₅=2.0×10¹⁴ cm³?mol^?1?s^?1) and C₂H+O=CH^?+CO (k ₆=3.6×10¹²exp(?10.9 kJ?mol^?1/RT) cm³?mol^?1?s^?1) and neglecting the C₂H+O₂=CH^?+CO₂ reaction.     

An IR spectroscopic study of liquid ozone and ozone dissolved in liquid argon

We have measured and interpreted the IR spectra of liquid ozone films at 78–85 K and ozone dissolved in liquid argon at 91–95 K. A less hindered rotation of ozone molecules in argon manifests itself as an intensity redistribution, caused by the Coriolis interaction, from the states ν₃(B ₁) and ν₁ + ν₃(B ₁) to the states ν₁(A ₁) and 2ν₁(A ₁), respectively. The occurrence of wings in the contours of the bands ν₁(A ₁), 2ν₁(A ₁), and 2ν₃(A ₁) in liquid Ar and their absence in the spectrum of O₃ also confirms the conclusion that the rotational motion of ozone molecules in an inert solvent at low temperatures is relatively less hindered. Maxima of ozone bands in Ar solution are shifted toward lower frequencies compared to those in the gas phase by 1–30 cm^?1, which corresponds to the following shifts of harmonic frequencies of the molecule: Δω₁ = ?1.85(5) cm^?1, Δω₂ = ?0.67(7) cm^?1, Δω₃=?7.20(5) cm^?1. It was found that the absorption band of the ν₃ mode in the spectrum of O₃ in the liquid phase has a complicated asymmetric contour because of the resonance dipole-dipole interaction. The first and second spectral moments of this band have been determined to be M ₁ = 1030.6 cm^?1 and M ² = 240.0 cm^?2.     

Tunable diode laser measurements of the band strength and collision halfwidths of nitric oxide

The strength of the fundamental absorption band of nitric oxide at 5.3 μm and collision halfwidths of nitric oxide lines broadened by nitrogen, argon, and combustion gases were measured in absorption cell, flat flame and shock tube experiments using a tunable diode laser. Room temperature absorption measurements were made in an absorption cell filled with NO/N₂ or NO/Ar mixtures or with probe-extracted combustion gases. High temperature (to 2500 K) absorption measurements were performed for NO in N₂ and NO in Ar using a shock tube, and for NO in combustion gases using a flat flame burner.Absorption measurements were made on lines from 1860–1925 cm^?1, ($\text{Ω=}\text{1}\text{2}$ and $\text{3}\text{2}$,P($\text{5}\text{2}$-R ($\text{29}\text{2}$)) resulting in a band strength of 123±8 cm^-2 atm^?1 at 273.2 K. Collision halfwidth dependencies for each broadening species were examined as a function of rotational quantum number and temperature.     

Formation of N2 C3Πu and B3Πg by dissociative recombination of Ar 2 + in Ar+N2 early afterglow

The hf pulse excited Ar + N₂ mixtures and early afterglow are investigated at total pressures from 266 to 1995 Pa using nitrogen of 0·05–0·5% concentration. The time-resolved intensity of Ar I atomic lines and N₂ (2nd pos., 1st pos. and 1st neg.) band systems exhibit an intense early afterglow (0·3 ms). Both the decay of electron densityn _e and that of molecular Ar ₂ ⁺ ions and enhancement of coefficient of dissociative recombination due to electron temperature decrease after the pulse lead to the formation of characteristic secondary maximum of Ar I spectral line and N₂ molecular band intensities in the momentt _m after cut-off the pulse. The values oft _m(B³_g)>t _m(C³_u)>t _m(Ar I) decrease with increasing total pressure and increase with growing concentration of N₂ in Ar. In the afterglow period the Ar ₂ ⁺ dissociatively recombine in 5p and 4p Ar states. As a result of radiative transitions the metastable Ar (³P_2,0) atoms are formed which consequently due to collisions with N₂ molecules create electronically excited N₂. With increasing nitrogen concentration this effect becomes less pronounced and at concentration of N₂ greater than 0·5% it is negligible.     

Radiative Transitions and Temperature Time Dependences in Pulse Excited Microwave Discharges – (N2, Ar + N2)

Quantitative spectral and microwave measurements of vibrational temperatures and electron densities were performed for 2400 MHz non-isothermic pulse excited discharges in flowing nitrogen and argon at pressures (60–2700) Pa. A detailed analysis of the N₂ vibrational states population for the N₂ C³Π_u, X¹Σ_g⁺ electronic states has been carried out. The basic difficulties encountered when comparing the spectroscopically determined values of vibrational temperatures with corresponding quantities of the ground electronics state are mentioned and the time resolved dependences of the translational gas temperature in N₂ during the microwave pulse is evaluated. The steady state in the nitrogen pulse excited microwave plasma is reached within 3 · 10^?4 s, but generally, this time depends on the gas pressure in the discharge tube. In the Ar + N₂ mixtures the excitation conditions are complicated by the metastable argon atoms (3P_2,0) creating the nonequilibrium populations of electronic, vibrational and rotational N₂ states.     

Resonance absorption and fluorescence in argon

Absorption cross sections of argon for argon resonance radiation have been measured by several techniques. The apparent cross sections are small (0·1 to 1·6 × 10^-18 cm²) for resonance absorption and the values depend on the technique used for measurement. These observations are interpreted in terms of extensive reversal and broadening in the source. The excitation and quenching of resonance fluorescence was studied to provide information about the rates of the processes

The rate constants were estimated relative to k _r, the rate constant for radiation. Radiation imprisonment leads to a reduction of k _r from its natural value and observations of the decay of resonance fluorescence suggest that k _r ～ 1·5 × 10⁵ s^-1 in our system at [Ar] = 2 × 10¹⁷ atom cm^-3. Combining this value with the relative values for the quenching rate constants gives k ₁ < 1·5 × 10^-13, k ₁′(M = N₂) ～ 6 × 10^-12, k ₁′(M = NO) ～ 4 × 10^-10, in units of cm³ s^-1 molecule^-1.     

Spectroscopic studies of a plasma temperature and radiation standard based on a wall-stabilized arc

The absolute determination of the axial temperature (12,000 K ≤ T ≤ 14,500 K, 0.9×10²³ m^-3 ≤ N_e ≤2.5×10^-3 m^-3 of a 3 mm bore wall-stabilized arc operating in argon at 1.75×10⁵ Pa is described using spectroscopic techniques both in the visible and vacuum u.v. spectral regions. Computer simulation techniques to predict the line wing correction for the A(I) line at 430 nm and a detailed study of sources of systematic error have been applied. The reproducibility of the temperature results and the establishment of LTE demonstrates the suitability of the source as a plasma temperature and radiation standard. A detailed study of the Stark broadening of H_β and the comparison of the experimental profiles with the theories of Kepple and Griem and Vidal, Cooper and Smith has shown the former giving N_e values some 11% lower and the latter 1% higher than the pure argon diagnostics at N_e ? 2 × 10²³ m^-3. New values for the argon transition probabilities of two lines and continuum factors at two wavelengths are presented.     

Spectroscopic Measurements of Plasma Temperatures in a Radio Frequency Discharge

Argon and mixtures of argon with CH₄, C₂H₂ and N₂ have been excited in a 27.2 MHz radio frequency discharge at pressures of 10 and 5 Torr. Plasma spectra have been recorded and analyzed. The excitation temperatures of Ar I and H, the C₂ and CN vibrational temperatures and the N₂ and CN rotational temperatures have been determined and discussed.     

Absolute intensity measurements of the CO2 bands 401III←000 and 411III←010

The absolute intensities of the transitions 401_III←000 and 411_III←010 of CO₂ have been measured from spectra obtained under high resolution. Both the vibration-rotation line intensities and the integrated band intensities are reported. The rotationless transition moment of 401_III←000 is deduced and a vibration-rotation interaction factor F(m) = 1+(4.92×10^?4)m+(4.4×10^?7)m² is determined. The values obtained are: S_Band(401_III←000) = (25.54±0.22)×10^?5 cm^?2atm_{(293 K)}^?1, |R₀₀₀^401_III| = (1.87±0.02)×10^?4D, and S_Band(411_III←010) = (1.83±0.13)×10^?5 cm^?2atm_{(293 K)}^?1.     

Influence of ultrashort laser pulse duration on the X-ray emission spectrum of plasma produced in cluster target

Line emission spectrum of a laser plasma produced in an argon cluster jet target was measured on the n ¹ P1?1¹ S ₀ (n=5–9) transitions of the helium-like Ar XVII ion for a pulse duration varying from 45 fs to 1.1 ps and a constant fluence of ～10⁵ J/cm². The independent modeling of the relative intensities of the transitions from the n=5,..., 10 levels, as well as of the 2¹ P ₁? 1² S ₀ and 2³ P ₁?1² S ₀ lines and dielectronic satellites indicates that the electron temperature is anomalously low and that the electron density in emitting plasma increases with shortening the laser pulse. The excitation from the ground state by a small fraction of hot electrons is expected to be the main channel of populating the Ar XVII levels.