CN Violet Research Articles

The Violet Opacity in the Red Peculiar Stars – III. Spectral analysis of the SC star GP Ori

Medium-resolution (1.5-2.5 A) spectrum has been obtained for SC star GP Ori in a wide range of wavelengths from 3730 to 6250 A. It is characterised mainly by strong atomic lines, as well as moderately strong bands of the CN violet system and CH (0,0) and (0,1) bands at 4315 and 4890 A. Weak bands of C2, C3, and ZrO molecules are observed, however, no evidence is found for the presence of either SiC2 (Merrill-Sanford bands) or YO. The most prominent atomic lines along with the NaID12 are those of CaII (K,H), CaI at 4227 A, SrI at 4607 A, SrII at 4077 and 4215 A, and BaII at 4554 A. Hβ seems to be in emission.

State-to-state and total rotational energy transfer rate constants for CN(B 2Σ+,v=0,N)+He and C2N2

Total rotational energy transfer (RET) rate constants, state-to-state RET rate constants, and radiative lifetimes have been measured for CN(B 2Σ+, v=0, Ni=0, 4, 6, 7, 8, 11 and 13). All experiments were conducted under single collision conditions in a static cell filled with previously prepared C2N2/He mixtures at various total pressures up to a maximum of 800 mTorr. The above initial states were prepared by pumping CN(X) with a pulsed dye laser tuned to appropriate frequencies in the P-branch of the CN-violet (0,0) band following the production of CN(X) by the excimer laser photolysis of C2N2 at 157 nm. Total RET rate constants and radiative lifetimes were determined from decay constants obtained with a transient digitizer over the above range of cell pressures. State-to-state RET rate constants were obtained from time-averaged fluorescence spectra in the R branch of the (0,0) band of the CN violet system at various cell pressures within the above range. A weak propensity for odd jumps in N was discernable in state-to-state RET rate constants in CN(B)/He collisions for N>4. Total RET rate constants varied only slightly with Ni for 0⩽Ni⩽19 with He as collision partner, but decreased monotonically with increasing Ni when C2N2 served as collision partner. No firm evidence for collisionally induced CN(B)↔CN(A) was apparent from our data.

The low-temperature afterglow in N 2 –ε·CH 4 gas mixtures

The influence of the small methane impurities on the pure nitrogen afterglow was studied in DC flowing plasma reactor in wide range of methane concentrations (0.01–400 ppm) at different wall temperatures of the reactor observation part (77–300 K). The relative vibrational distributions of $${\text{N}}_{\text{2}} ({\text{C}}^{\text{3}} \Pi _u ){\text{ and N}}_{\text{2}}^{\text{ + }} ({\text{B}}^{\text{2}} \sum _{\text{u}}^{\text{ + }} )$$ states have been calculated from the recorded spectra in pure nitrogen. We observed strong quenching of the nitrogen pink afterglow at methane concentrations of a few ppm, however the pink afterglow intensity was growing up at the methane concentrations under 1 ppm. Simultaneously, the maximum pink afterglow intensity was observable at later decay times with the increase of the methane concentration. At low wall temperatures, especially at later decay times, we observed extremely high sensitivity of the pure nitrogen to the methane pretence in the discharge. Thus we are able to detect the methane concentrations in order of 0.01 ppm. We also observed the higher transitions of the CN violet system which are usually observed in the spectra of space emission sources. The method detecting hydrocarbon and fluorocarbon impurities in pure nitrogen is based on the results of the above mentioned experiments. We present first results of some experiments studying the polyhydrocarbon destruction rates measured by this new sensitive method. Finally, we designed also the simple kinetic model describing the processes during the afterglow in the N2–e·CH4 mixture.

Measurement of carbon atom density in the flowing afterglow of a CH 4−N 2 microwave plasma

Optical emission spectroscopy in a flowing afterglow of a CH 4(0.01–0.075%)-N 2 microwave plasma is used to measure absolute carbon atom concentrations. From the intensities of the nitrogen first positive and of the CN violet bands, and by means of a kinetic mechanism, the C atom concentration is found to be in the range 1–13 × 10 13cm −3 at 180 W and at pressures between 12.5 and 50 mbar. An increase of C concentration versus flow time is observed, indicating that the major part of the C atom density is produced along the afterglow.

Vacuum Ultraviolet and Visible Optical Emission Spectra from Laser Ablation of Graphite at 193 NM: Application to Carbon Nitride Thin Films Deposition

AbstractOptical emission spectra in the ultraviolet and visible range (110-600 nm) were recorded during pulsed ArF laser ablation of graphite targets in vacuum and in low pressure N2 atmospheres. During graphite ablation in vacuo, the recorded spectrum consists only of several atomic lines lying below 300 nm. They are due to radiative transitions from upper carbon excited states down to the fundamental one. The most intense atomic lines are observed at 247.85 nm and near 165.5 and 156 nm. During ablation in increasing nitrogen pressure, the spectra are quickly dominated by the bands of the CN violet system whereas the intensity of the atomic lines only slightly increases. We have observed the bands corresponding to the vibrational sequences Δv = +1 (358.4-369.7 nm), Δv = 0 (384.7-394.4 nm) and Δv = -1 (414.3-421.6 nm). They already appear at nitrogen pressure as low as 0.05 mbar. Their intensity reaches a broad maximum between 0.5 and 0.8 mbar and slowly decreases.Taking into account the results of this optical study, the deposition of carbon nitride thin films has been undertaken. The surface analysis by X-ray photoelectron spectroscopy (XPS) of the obtained C1-xNx deposits shows a correlation law between the nitrogen incorporation (x) and the pressure of nitrogen.

Evidence for CN in spectroscopic studies of laser-induced plasma during pulsed irradiation of graphite targets in nitrogen and ammonia

Mass- and time-integrated optical emission spectra were recorded during direct XeCl laser ablation (308 nm, 30 ns) of graphite targets in and in atmospheres at various pressures and at different laser fluences . Spectra in vacuo were also acquired. The optical emission spectra of the laser-induced plasma are characterized by strong molecular emission bands of and CN and by lines of atomic ions . At the highest pressures the spectra are dominated by a Swan system (vibrational sequences ) and a CN violet system . Their intensities increase with an increase of gas pressure. Mass spectrometry was also performed on the ablated materials and various chemical species were found; the most common ones were C, CN and .

Optical Emission Diagnostic of Laser-Induced Plasma during CNX Film Deposition

To investigate the characteristics of the plasma plume created by reactive laser ablation (RLA) of graphite, optical emission spectra (OES) of the ablated species were recorded for different distances from the target, for various laser fluences and for several N2 pressures. The spectra were dominated by the molecular bands of C2 and CN radical: C2 Swan and CN violet spectral systems. From the molecular band intensities the rotational and vibrational temperatures of CN radicals were derived though there is not a significant dependence of the temperature with fluence, a strong increase of intensity can be observed with the increase of the laser fluence.

Spectroscopic studies during pulsed laser ablation deposition of C–N films

Mass and optical emission spectra were recorded during XeCl laser ablation of graphite targets in vacuo and in low pressure (up to 2.5 mbar) N2 and NH3 atmospheres to study the role of gas phase reactions in C–N compound formation. Mass spectra were recorded during ablation in vacuo (10−6 mbar) and in N2 at 1×10−4 mbar. In vacuo, during the first stage of ablation, the mass spectrum was characterized by the peaks at 12 and 26 amu (C and CN). The CN peak intensity was slowly decreasing with the laser pulse number, to disappear after ∼3000 laser pulses. In contrast, the peak at 26 amu is permanent during the whole ablation when N2 is introduced in the chamber. The optical emission spectra recorded during ablation in vacuo are dominated by the bands of the C2 Swan system. Weak bands from CN can also be distinguished. Spectra recorded during ablation in NH3 are also dominated by the bands of the C2 Swan system. During ablation in N2 (10−4–2.5 mbar), strong bands of the CN violet system are detected. Their intensities increase with increasing N2 pressure and, at the same pressure, with increasing laser fluence. It was observed that the N atom density recorded in the deposited C–N films is increasing with the intensity of the CN emission.

Measurement of Rotational Temperature by Simulated Molecular Spectra

Abstract The measurement of temperature of heavy particles in a thermal plasma is based on the comparison of experimental rotational spectrum obtained by optical emission Spectroscopy and synthetic spectra calculated for different temperatures. The calculation principle of the synthetic spectra is detailed as well as the temperature accuracy obtained. This method is used to measure the temperature of an Ar-CO2 mixture plasma produced in a wall stabilized arc with molecular spectra of C2 (Swan system) and CN (violet system).

Determination of C-atom density downstream an Ar-CH4 rf plasma torch

Nitrogen, oxygen, and carbon atoms have been detected by optical emission spectroscopy in a common flowing post-discharge of an Ar-x CH4 rf plasma torch and an Ar-2%N2 microwave discharge. Gas temperature as determined from CN and N2 rotational svstems is 3200 ± 200 K in the rf torch and 700 ± 100 K in the post-discharge at a time 3 X10−2 s after the rf plasma torch. From the intensities of the N2 1st positive system, of NO, and of CN violet hands, the atom densities have been determined as 2 X 1016 cm3 for N, 1015 cm3 for O, and 6 X 1012 cm3 for C in the post-discharge at p=650 torr, with 103 of CH4 in the Ar torch.

Direct measurement of thermal rate constants for state-to-state rotational energy transfer in collisions of CN(X 2Σ+, v=2, N) with He

Stimulated emission pumping state preparation and laser induced fluorescence state detection in the CN(B 2Σ+–X 2Σ+) violet system have been employed to study relaxation of single rotational states of CN(X 2Σ+, v=2) in collisions with He at 295 K. Approximately 2/3 of the value of the total removal rate constant for CN(X 2Σ+, v=2, N=2, 11, or 14) corresponds to changes in the rotational quantum number of ‖ΔN‖≤3 and a strong propensity is evident which favors even changes in N for ‖ΔN‖≤4. The measured rate constants are consistent with detailed balance, can be described with statistical power-gap and exponential energy-gap fitting functions and, where compared, are in accord with an IOS-based scaling function. No significant difference is found between a sum of state-to-state rate constants and separately measured total removal rate constants for N=2, 11, and 14. The total removal rate constants decrease monotonically between N=0 and N=41 to about 1/3 of their value at N=0.

Optical emission from the laser-induced plasma during excimer laser etching of diamondlike carbon films

Optical emission from the laser-induced plasma plume produced during KrF (248 nm) excimer laser etching of diamondlike carbon films has been characterized. The emission spectrum in the visible and UV wavelength regions is dominated by the C2 Swan bands (d3Πg−a3Πu), CN violet bands (B2 Σ+−X2 Σ+), and a continuum emission in the 500–700 nm range. The emission intensities of the major bands are a strong function of film density. Higher emission intensities are observed during the etching of low-density films. The molecular vibrational temperatures for C2 and CN radicals, calculated from the emission intensities, are in the range of 10 000–20 000 K.

Study of CN emission from a laser induced plasma of graphite in air

Emission of neutral N atoms and CN molecules has been studied in the plasma produced by focusing a 200 mJ Nd: YAG laser onto a graphite target in air. Emission of atomic fines appears at early times. The Stark broadening of these lines is strongly time dependent due to the evolution of electron density in the plasma. At later times the spectrum is dominated by the CN violet system B 2Σ- X 2Σ. In the range from 1 to 20 μs the population of B 2Σ rovibrational levels can be described by a temperature of about 8500 K.

External magnetic field effects on chemiluminescence intensities from C 2(d) and CN(B) states in low pressure C 2H 2/N, O flames

Magnetic field effects on chemiluminescence intensities from some reaction intermediates in low pressures C 2H 2/N, O flames were measured. O atoms were produced without O 2 by adding NO into a discharged N 2 stream. Diffusion flames were formed between electromagnet poles when a C 2H 2 stream from another inlet encountered an N 2 stream containing O and/or N atoms. Both partial titration by and excess addition of NO enhanced the magnetic field quenching of the chemiluminescence due to the C 2 Swan system. The CN violet showed magnetic field quenching only when the excess NO was present. Possible mechanisms for these magnetic field effects are discussed briefly.

Temperature measurements from CN spectra in a laser-induced plasma

The spontaneous-emission spectra of the CN violet system were observed following excimer-laser-induced breakdown of an atmospheric-pressure CO 2/N 2 mixture. Using a triple monochromator and a gated linear-diode array, the spectra were acquired with spectral resolutions of 2 and 7 cm -1 within 1 μsec following the laser pulse. Comparison of the observed rotation-vibrational structure of the Δν=0 sequence and the synthetic spectra, which were calculated using direct diagonalization of the rotational and fine-structure Hamiltonians, yielded internal, molecular temperatures of approx. 8000 K. No evidence of internal nonequilibrium of the rotational and vibrational modes was observed.

Dicyanoacetylene photodissociation at 193 nm and at 248 nm studied by transient absorption spectroscopy. Production of CN, C 2 and C 3N

Laser photolysis of dicyanoacetylene at 193 nm and at 248 nm, leading to the production of CN, C 2 and (probably) C 3N, has been investigated. CN violet bands and C 2 Swan bands were observed in absorption. Photolysis at 193 nm produces CN in both the X 2Σ + and in the 2Π i manifolds, the latter — probably populated via a two-proton process — being revealed by a delayed (collision-induced) population of higher vibrational levels of the ground electronic state. Photolysis at 248 nm is an efficient two-photon process. It is still not clear what mechanism is responsible for the formation of the C 2 molecule at 193 nm. Throughout the paper, the theoretical of Sadlej and Roos helped to choose the optimal interpretation of the experiments.

Titan atmospheric composition by hypervelocity shock-layer analysis

The Cassini Mission, a NASA/ESA cooperative project which includes a deployment of probe into the atmosphere of Titan, is described, with particular attention given to the shock radiometer experiment planned for the Titan probe for the analysis of Titan's atmosphere. Results from a shock layer analysis are presented, demonstrating that the mole fractions of the major species (N2, CH4, and, possibly Ar) in the Titan atmosphere can be successfully determined by the Titan-probe radiometer, by measuring the intensity of the CN(violet) radiation emitted in the shock layer during the high velocity portion of the probe entry between 200 and 400 km altitude. It is shown that the sensitivity of the CN(violet) radiation makes it possible to determine the mole fractions of N2, CH4, and Ar to about 0.015, 0.003, and 0.01, respectively, i.e., much better than the present uncertainties in the composition of Titan atmosphere.

Baseline shifts in inverse Zeeman-effect graphite furnace atomic absorption spectrometry ascribed to the Zeeman effect of the CN molecule

The background-corrected Zeeman absorbance baseline shows shifts for lines of several hollow cathode lamps up to tenths of an absorbance unit with firings of an empty graphite furnace atomiser and clear differences in the sizes of the shifts according to whether the furnace is purged with nitrogen or argon. Baseline shifts are seen for hollow cathode lines close to listed rotation lines of the (0,0) and higher bands of the CN violet system. Such shifts, it is suggested, are caused by overlap of the hollow cathode lines with Zeeman-shifted CN lines and in support of this suggestion the known behaviour of CN lines in magnetic fields (spin doublet contraction) is cited. Evidence is presented for the existence of interfering CN lines near the main atomic absorption line of Cr (357.9 nm), as a spectral interference occurs in both the inverse Zeeman configuration (with lamps containing iron) and with continuum source correction.

Spectroscopic Detection of Oxygen in Nitrogeneous Gas Mixtures

AbstractA pulsed high‐frequency discharge was used to excite a non‐LTE (local thermal equilibrium) plasma with a high specific power density sufficiently high to dissociate oxygen and gaseous oxides. If traces of hydrocarbons were present in the gas mixture, in the spectrum the Violet system of CN appeared with a long radiation decay time. The CN bands are excited preferentially by inelastic collisions with metastable nitrogen molecules (A3σ). These levels can be efficiently depopulated by competing impact with atomic oxygen. By measuring the radiation signal during the radiation decay a dynamic range of 6 was achieved for a variation of the oxygen content between 1 and 100 ppm.The measured radiation decay of the violet CN 0–0‐bands at 388 nm was simulated by a simple model of rate equations valid in the time region where diffusion processes may be neglected.

Single rotational state preparation and relaxation in CN(X 2Σ +, ν=2). Stimulated emission pumping and laser-induced fluorescence detection

Stimulated emission pumping (SEP) in the CN(B 2Σ +−X 2Σ +) violet system has been employed to prepare substantial populations of CN(X 2Σ +, ν=2) molecules in single rotational states. These populations are detected by laser-induced fluorescence (LIF) and the combined SEP-LIF procedure is used to observe the population decay of the prepared states in collisions with helium atoms.