Lifetime measurements on electronically excited C2(A1Πu) and C2(d3Πg) by laser-induced fluorescence

Bauer, Werner; Becker, K. H.; Bielefeld, M. J.; Meuser, R.

doi:10.1016/0009-2614(86)87008-7

Cited by 45 publications

(10 citation statements)

References 10 publications

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“…In the detailed discussion of their lifetime data, which became available at the conclusion of our analysis, Bauer et al (1986) obtain / 02 = 2.9x10" 3 for a trial ER 2 function providing a good fit to the lifetimes. An alternative function providing an almost equally good fit to the lifetimes gives / 02 =1.8Xl0" 3 .…”

Section: Ii) Oscillator Strengthsmentioning

confidence: 78%

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The chemical composition of carbon stars. I - Carbon, nitrogen, and oxygen in 30 cool carbon stars in the Galactic disk

Lambert¹,

Gustafsson²,

Eriksson³

et al. 1986

ApJS

371

357

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The chemical compositions of 30 Galactic carbon stars are determined from high-resolution infrared (1.5-2.5 ¡im) spectra and new model atmospheres. Elemental C, N, and O abundances (with respect to hydrogen) are obtained from lines of the C 2 Phillips system's Ay =-2 sequence, the CN red system's Ay =-2 sequence, and the CO X l '2 + vibration-rotation second-overtone bands. The 12 C/ 13 C ratios are extracted from the CN Ay =-2 sequence and, in two semi-independent ways, from the CO first-and second-overtone bands. Metal abundances are determined from a handful of atomic fines. Spectra at 3-4 jüim for a few stars provide additional fines which are used as checks. These include the HCN 3 fim bands, the CN red system's Af =-3 sequence, and the NH X 3 2and the CH X 2 U fundamental vibration-rotation bands. The H 2 1-0 S(0) fine near 2.22 ^m is also available as a check. Model atmospheres accounting for the fine blanketing by the poly atomics HCN and C 2 H 2 were computed for a grid of effective temperatures and surface gravities. Selected models for differing opacities and assumptions (e.g., surface heating) were computed. Effective temperatures are on the scale established by lunar occultation angular diameters. The surface gravity is based on a mean stellar mass and absolute luminosity. The principal results are as follows: 1. The dispersion in C, N, and O abundances for the 30 program stars is small. 2. The stars show only modest carbon enrichments; the most carbon-rich star has C/O-1.6, and about 50% of the stars in the sample have C/O <1.1. 3. The 13 C abundance is, in general, low, with 30< 12 C/ 13 C < 70 encompassing the larger part of our sample, and the very 13 C-rich (12 C/ 13 C-4) stars are the exceptions, not the rule. 4. The oxygen abundances are, in general, slightly subsolar and in good agreement with results for M and MS giants (progenitors) and carbon-rich planetary nebulae (descendants). 5. The nitrogen abundances are subsolar and below the values measured for M and MS giants and planetary nebulae. This difference may reflect an error in the CN dissociation energy or possibly in the effective temperature scale. 6. The metal abundances are approximately solar. 7. The weak H 2 fines are not evidence for hydrogen-deficient atmospheres. It is shown that the observed CH fine strengths are less than the predicted strengths. This discrepancy is discussed but not resolved. Possible explanations include non-LTE effects in the excitation and/or formation of CH, strengthened by thermal inhomogeneities, and a significant underestimate of the effective temperature scale. For the typical star with a low 13 C content, conversion to a carbon star was achieved by addition of pure 12 C, a product of helium burning, to the envelope of a typical G, K, or M giant. The 13 C-rich stars are not nitrogen-rich and, therefore, may not have undergone severe exposures to the hydrogen-burning CNO cycles. It is shown that the abundances may be used to calibrate published spectrophotometric indices of C 2 , CO, and CN bands. Suc...

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Section: Ii) Oscillator Strengthsmentioning

confidence: 78%

“…lifetimes of vibrational levels in the A state Bauer et al 1985Bauer et al , 1986, and a determination of the relative /-value of the Phillips and Swan systems using an absorption tube and high-resolution spectrometer (Davis et ai 1984). Other older experimental results are referenced by Erman et al (1982).…”

Section: Ii) Oscillator Strengthsmentioning

confidence: 99%

The chemical composition of carbon stars. I - Carbon, nitrogen, and oxygen in 30 cool carbon stars in the Galactic disk

Lambert¹,

Gustafsson²,

Eriksson³

et al. 1986

ApJS

371

357

View full text Add to dashboard Cite

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“…Experimental lifetimes of specific vibronic states of C 2 have been reported by Smith (1969); Curtis et al (1976); Bauer et al (1985Bauer et al ( , 1986; Naulin et al (1988); Erman & Iwame (1995) and Kokkin et al (2007). These observations provide an important test of any spectroscopic model for the system.…”

Section: Introductionmentioning

confidence: 76%

“…We have computed life times of C 2 for all rovibronic states below 30 000 cm −1 . These are compared to the experimental and theoretical values by Smith (1969); Cooper & Nicholls (1975); Curtis et al (1976); Bauer et al (1985Bauer et al ( , 1986; Naulin et al (1988) and Erman & Iwame (1995).…”

Section: Lifetimementioning

confidence: 98%

ExoMol line lists XXXI: spectroscopy of lowest eights electronic states of C2

Yurchenko

Szabó

Pyatenko

et al. 2018

Monthly Notices of the Royal Astronomical Society

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Accurate line lists for the carbon dimer, C 2 , are presented. These line lists cover rovibronic transitions between the eight lowest electronic states: energy curves (PECs) and transition dipole moment curves are computed on a large grid of geometries using the aug-cc-pwCVQZ-DK/MRCI level of theory including core and core-valence correlations and scalar relativistic energy corrections. The same level of theory is used to compute spin-orbit and electronic angular momentum couplings. The PECs and couplings are refined by fitting to the empirical (MARVEL) energies of 12 C 2 using the nuclear-motion program Duo. The transition dipole moment curves are represented as analytical functions to reduce the numerical noise when computing transition line strengths. Partition functions, full line lists, Landé-factors and lifetimes for three main isotopologues of C 2 ( 12 C 2 , 13 C 2 and 12 C 13 C) are made available in electronic form from the CDS

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“…These estimates depend on the | R e | 2 's for the permitted transitions. Since the | R e | 2 for the Swan system is well determined from lifetime measurements and the |RJ 2 for the Ballik-Ramsay system is only a weak contributor to the \R e \ 2 of the intercombination transitions, the |R e | 2 for Phillips system is the leading source of uncertainty: lifetime measurements for the A 1 II M state (Bauer et al 1985(Bauer et al ,1986) yield a | R e | 2 that differs by almost a factor of 2 from the series of fairly concordant theoretical predictions (see summary by O'Neil, Rosmus, and Werner 1987). This uncertainty translates to about a 50% uncertainty in | R e \ 2 X but a larger uncertainly in I Re \cX • Estimates of | R e \ 2 X by this method are smaller than the estimates obtained from fits of synthetic and observed spectra, and the band ratio R. Estimates of [RJ 2 * overlap the range suggested by the fit to the observed spectra.…”

Section: Rotational Excitation Of C 2 A) Predicted Populations Anmentioning

confidence: 99%

High-resolution spectroscopy of the C2 Swan 0-0 band from Comet P/Halley

Lambert¹,

Sheffer²,

Danks³

et al. 1990

ApJ

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High-resolution (À/AÀ ^ 80,000) spectra of the C 2 Swan system's 0-0 band from comet P/Halley in 1986 March show that the populations of the upper (d 3 11^) state's rotational levels may be described by two rotational temperatures. The low rotational levels (J'< 15) provide a low temperature: 7^o t ~ 600-700 K. The higher levels correspond to ~3200 K. If a contribution from the "3200 K" molecules is subtracted from the populations of the low-J' levels, the latter are characterized by the low-temperature 7^o t ~ 190 K.A comparison with recent predictions for C 2 molecules fluorescing in sunlight shows that the observed and predicted level populations are in good agreement for J' > 15, but there is a sharp disagreement for the low rotational levels: the observations show that the 3 n o , 3 n i5 and 3 II 2 substrates at low J' have very similar populations and an identical 7^o t to within the errors of measurement, but, by contrast, the predictions give three quite different forms for the run of population with J' for these substates. It is argued that the addition of the previously overlooked satellite transitions within the Swan system to the fluorescence studies may reproduce the observed populations at low J' and yet leave unaffected the agreement between predicted and observed populations at high J'. It is also noted that the observed line fluxes may include a contribution from freshly formed molecules that have yet to achieve fluorescence equilibrium.

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Lifetime measurements on electronically excited C2(A1Πu) and C2(d3Πg) by laser-induced fluorescence

Cited by 45 publications

References 10 publications

The chemical composition of carbon stars. I - Carbon, nitrogen, and oxygen in 30 cool carbon stars in the Galactic disk

The chemical composition of carbon stars. I - Carbon, nitrogen, and oxygen in 30 cool carbon stars in the Galactic disk

ExoMol line lists XXXI: spectroscopy of lowest eights electronic states of C2

High-resolution spectroscopy of the C2 Swan 0-0 band from Comet P/Halley

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