CN Emission Research Articles

Some remarks on the dynamics of deformable bodies.

factor of 2 appear in the nonequilibrium region, thus illustrating the uncertainties regarding the behavior of species other than CN. Except for their equilibrium levels, the curves for N and NO are omitted from the figure for clarity, but their behavior in time and magnitude is similar to that of 0 and CN, respectively, and in good agreement with the 16-reaction system. It is also shown in Ref. 1 that both the experimental data and the computed results follow binary scaling laws in the nonequilibrium region. Hence, the effects of varying ambient density are accurately reproduced, and it is only necessary to compare results obtained with the two chemical models at other shock speeds and gas mixtures. For these comparisons, the magnitude and time of the peak intensity are indicative of the adequacy of the 9-reaction system, and if they agree with the data, the remainder of the intensity profile is also found to be matched. The variation of the peak CN intensity over the range of shock speeds considered was computed using the 9-reaction system of Table 1 and is compared with computations using the 16-reaction system and experimental data in Fig. 2. The results show the predictions made with the 9and 16-reaction systems to be similar in the speed range from 5.8 to 7.0 km/sec, which is that of primary interest for Mars entry. The computed and experimental times to peak CN intensity are shown in Fig. 3. Again, the results for both reaction systems are similar and provide a good approximation to the experimental data. The foregoing results indicate that the predictions based on the simplified chemical model of 9 reactions presented in Table 1 are adequate for estimating the nonequilibrium radiant emission of CN in shock-heated mixtures of C02 and N2 for the range of speeds of current interest for entry into the Martian atmosphere.

Mechanisms of Populating Electronically Excited CN in Active Nitrogen Flames

CN red (A 2Π⇀X 2Σ) and violet (B 2Σ⇀X 2Σ) bands radiated from active nitrogen flames with halogenated hydrocarbons and with cyanogen derivatives have been studied at pressures from 0.013 to 100 torr. Intensity measurements have shown that there are three distinct vibrational population distributions P1, P2, and P3 in the A 2Π state and corresponding distributions P1′, P2′, and P3′ in the B 2Σ state of CN. At very low pressures, P1 distributions are characteristic of cyanogen derivative flames and P2 distributions are characteristic of halogenated hydrocarbon flames. P3 distributions are most easily observed at pressures above 1 torr and with trace amounts of fuels containing carbon. Three distinct mechanisms responsible for producing these three types of distributions are proposed; two mechanisms involve the transfer of energy derived from the recombination of atomic nitrogen and the third is a chemical reaction using atomic nitrogen. Vibrational relaxation is observed for the P2 and P1′ distributions. Small amounts of oxygen are found to increase greatly the CN emission at low pressures. Intensity measurements of rotational lines in the red bands and in the violet 0, 0 band have been made as a function of pressure in CH2Cl2 flames. In the A 2Π state at pressures above 4 torr, a rotational temperature of 340°K can be defined, but below 4 torr the rotational distribution is best represented by a sum of two Boltzmann distributions. The effect of pressure on the amount of CN in the two distributions leads to a measured cross section of 15 Å2 for the effective collisional relaxation of rotation. From a study of the violet 0, 0 band, several new pairs of rotationally perturbed lines are found at low pressures. The formation rate of the A 2Π state relative to the B 2Σ state and to the X 2Σ state is obtained from the intensity ratio of main lines relative to extra lines in rotational perturbed pairs. CN is found to be formed in the A 2Π state at least 30 times more readily than in the B 2Σ state and about four times faster than in the X 2Σ state.

Calculation of molecular band spectra assuming a gaussian line profile

A method for computing molecular band spectra is described. The integrated intensity of each rotational line considered is distributed spectrally by forcing it to fit a gaussian line profile centered at the computed wavelength for the rotational line. The spectrum is then produced by linearly combining the dispersed rotational lines. The method is applied to CN(violet) emission and found to give an excellent qualitative description of the electronic band shape down to a resolution of about 1·0 Å and good quantitative agreement with (0,1) band shock tube measurements.

Kinetics of reactions involving CN emission. II. The reaction between oxygen atoms and cyanogen

The reaction between oxygen atoms and cyanogen has been studied in a flow system at temperatures up to 400 °C in the pressure range 1.0 to 5.0 mmHg. This reaction is first order in both reactants, and has an activation energy of 11.0 ± 2.0 kcal/mole; this is associated with the initial attack of an oxygen atom on cyanogen for which the exponential factor is close to 4 x 10 13 cm 3 mole -1 s -1 . It has not been possible to choose between mechanisms in which the initial steps are O + C 2 N 2 = NCO + CN (6) and O + NCO = NO + CO, (7) or O + C 2 N 2 = NCN + CO (8) and O + NCN = NO + CN. (9) Subsequent reactions include CN + NO = CO + N 2 , (11) O + CN = N + CO. (12) In the presence of molecular oxygen reactions (10) and (7) become important CN + O 2 = NCO + O. (10) Strong CN emission accompanying the reaction is shown to be largely due to the reaction O+O+CN = O 2 + CN*. (20) Quenching of this emission by various additives is associated with their reaction with CN for which relative rate constants are deduced.

Kinetics of reactions involving CN emission. I. General features of reactions with active nitrogen and atomic oxygen

Emission of the CN red (A -> X) and violet (B -> X) systems accompanying the reactions of active nitrogen with cyanogen, hydrogen cyanide, cyanogen chloride and methylene chloride and of oxygen atoms with cyanogen have been investigated. Bayes’s classification of the rod emission into the vibrational distributions P 1 (v' ≤ 3) and P 2 (v' ≥ 3) can be extended to the violet system, emission from levels 15 ≥ v' ≥ 5 accompanying the P 1 distribution and emission from level v' = 0 occurring with the P 2 emission. It is shown that the P 1 distribution and the excitation of the high vibrational levels of the violet system are due to collisions of CN with energetic species or CN acting as a third body for atomic recombination. The P 2 distribution is associated with the formation of electronically excited CN in exothermic transfer reactions such as N + CH = NC + H, N + CCl = NC + Cl

A STUDY OF THE CN EMISSION FROM ACTIVE NITROGEN FLAMES

When organic compounds are added to active nitrogen, the red and violet bands of the CN radical are emitted. The relative intensities of these red bands have been measured for a variety of added compounds, temperatures, and pressures. It is shown that there are at least three processes producing electronically excited CN radicals, two yielding CN(A2II) and one yielding CN(B2∑). The behavior of the flames indicates that a chain mechanism is involved. Adding ammonia, which does not react with nitrogen atoms, quenches the CN emission and inhibits the consumption of nitrogen atoms. It is concluded that a second reactive species in active nitrogen, possibly metastable N2(A3∑) molecules, initiates the reactions which result in light emission.

Excitation Temperatures from the CN Emission from the Low Chromosphere

Microphotometer tracings have been made of the region of the CN 3883 A band system, which is a prominent feature of the flash spectrogram obtained by Redman at the 1952 eclipse. The CN bands are seriously affected by blending, but enough unaffected lines have been found to enable the rotational intensity distribution in the 0–0 band to be measured at three heights below about 400 km. Self absorption is important, particularly at the band heads, and its effects have been estimated. The measurements indicate a negative excitation temperature gradient, the temperature at about 400 km being ≃4500°, and the value of the gradient uncertain. However, the CN emission may not be inconsistent with the positive kinetic temperature gradient of de Jager's most recent chromospheric model, if departures from local thermo-dynamical equilibrium and the imperfection of the observational data are taken into account.

C2 and CN Emission in the Shock Tube

C2 and CN Emission in the Shock Tube

A Study of the Monochromatic Polarization of Comet Arend-Roland (1956 h)

Measurements of the polarization of the Comet Arend–Roland have been made using combinations of glass and gelatin filters isolating respectively the continuum near 4530 A and the (0, 0) CN emission band near 3850 A. Measurements in the continuum extend over a range of phase angle of 26° and give polarizations between 5 and 20 per cent. There is reasonable agreement between the polarization curve of the Comet in the continuum and that for a metallic meteorite. Measurements on the CN emission band show that the plane of polarization is along the radius vector from Comet to Sun, and the amount of polarization is consistent with a fluorescence mechanism.

CN Bands in the Chromosphere.

view Abstract Citations (6) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CN Bands in the Chromosphere. Pecker, J. -C. ; Athay, R. G. Abstract CN bands are observed in emission in the chromosphere between the photospheric limb and a height of 750 km. Spectrograms obtained by the High Altitude Observatory at the Khartoum eclipse in 1952 showed a scale height of 210 km for the intensity of the emission in the 2 2 (0, 0) band at X 3883. The emission spectrum at 100 km gives a rotation temperature of 4500 , and the photospheric absorption spectrum in the Utrecht Atlas gives a rotation temperature of 4000 . At eclipse heights other than 100 km, the data were used to determine the temperature gradient. The rotation temperature was found to increase with height. Photospheric and chromospheric models were used to predict the absolute intensity of the CN emission in this band. The predicted intensity was less than the observed intensity by a tactor of 20. The discrepancy was accounted for by uncertainties in the absorption coefficient, which was obtained from a study of the absorption profile in the Utrecht Atlas. Publication: The Astrophysical Journal Pub Date: March 1955 DOI: 10.1086/145998 Bibcode: 1955ApJ...121..391P full text sources ADS |

THE DISTRIBUTION OF ENERGY IN THE VIOLET CN BANDS IN THE SPECTRA OF COMETS 1914B (ZLATINSKY) AND 1915A (MELLISH)

The spectra of Comets 1914 b (Zlatinsky) and 1915 a (Mellish) as photographed at the Lowell Observatory are shown in Figure 1. It is evident that the pair of bands (00) (11) of the CN violet system in Comet Mellish lie within the corresponding pair in Comet Zlatinsky. Particular attention was directed to this observation by Dr. V. M. Slipher in Lowell Observatory Bulletin No. 74, Vol. II, No. 24. The situation remains unaltered even after correction for the radial velocities of the comets relative to Earth. This circumstance denies the existence of a Maxwell-Boltzmann distribution of molecular population over the various rotational states, and consequently limits the significance of the temperature concept in the rarefied gases of a comet, where molecular collisions are rare. This restriction on comet temperatures was observed in another connection by K. Wurm.1 He found that temperature determinations of comets from the C2 and CN bands are contradictory on the assumption of a Maxwell-Boltzmann distribution. It would therefore seem, as Wurm concludes, that the absence of collisions would soon reduce the molecular population to the ground state of vibration and rotation apropos of the possession by CN of a permanent electric moment and its consequent ability to radiate vibrational and rotational quanta. This naturally leads to the belief that excitation of the comet CN molecules by sunlight will proceed from the ground state, and that the CN emissions will therefore shrivel into clusters of a few lines each in the immediate vicinity of the band origins, creating the impression of somewhat broadened lines.