Radiative and predissociation probabilities for individual rotational levels of the B 2Sigma state of CH with application to the radiative recombination of CH in the interstellar medium

Brooks, N. H.; Smith, W. H.

doi:10.1086/153269

Cited by 21 publications

(6 citation statements)

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“…We calculated line positions of other satellite branches after we calculated B state energy levels using the line positions of the main branch lines and X state energy levels. For an oscillator strength value, we used 3.1 ± 0.2 x 10-3, which was derived from an average of four lifetime measurements (Brooks and Smith, 1974;Anderson et al, 1975;Brzozowski et al, 1976;Ortiz and Campos, 1982). The ratio of adopted oscillator strengths for the B-X (0-0) and A-X (0-0) bands is 0.61, which is in excellent agreement with experimental values (Linevsky, 1967;Garland and Crosley, 1985) and a theoretical estimate (Hinze et al, 1975).…”

Section: Modelingsupporting

confidence: 66%

High-Resolution Spectroscopy of the A-X and B-X System of CH in Comet Austin (1990 V).

Kim

Brown²,

Spinrad³

1997

J. geomagn. geoelec

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We analyzed the A-X(0-0) band of CH, which appears in high-resolution spectra of comet Austin (1990 V), in order to understand fluorescence and collisional processes that influence the rotational structure of the A-X(0-0) band. Some of the weak lines of the A-X (0-0) band are clearly resolved, which have not been previously resolved with relatively low-resolution spectroscopy. We unambiguously confirmed the B-X (0-0) band lines around 3890 A, which had been suspected previously, but it had not been clearly identified because of strong adjacent CN and C3 bands. In order to analyze the cometary spectra we have conducted two different fluorescence calculations: a single-cycle fluorescence and fluorescent equilibrium. The fluorescent equilibrium model includes infrared and ultraviolet fluorescence processes as well as electron and neutral collisional effects, and therefore the model is a function of cometocentic distance. We found that single-cycle fluorescence models with a Boltzmann distribution in the X state fit the observed spectra better than the fluorescent equilibrium models. However, single-cycle fluorescence models with two different temperatures (130 K for F1 state and 250 K for F2 state) in the X state fit the Austin spectra significantly better than the single-cycle fluorescence model with the same temperature (150 K) for F1 and F2 states. This suggests that we are observing two different Boltzmann distributions of nascent, shortlife CH radicals right after they were produced by photodissociations of parent molecules. We presented g-factors of the A-X (0-0) and B-X (0-0) bands as a function of heliocentric velocity based on single-cycle fluorescence models with a 150 K distribution in the X state. We have calculated the expected intensity of the fundamental band (v" = 1 --+ 0) of CH and discussed the detectability of this band near 2730 cm-1. We also discussed possible parent molecules of CH and long lifetimes of the parent molecules, which may explain extensive emissions of CH up to 105 km from the nucleus despite its short lifetime.

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Section: Modelingsupporting

confidence: 66%

High-Resolution Spectroscopy of the A-X and B-X System of CH in Comet Austin (1990 V).

Kim

Brown²,

Spinrad³

1997

J. geomagn. geoelec

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“…For the CH molecule, predissociation is expected for the A, B, C, and D states. Predissociation was first observed in the laboratory by Shidei (1936) and confirmed by Herzberg & Johns (1969), and Ubachs et al (1986) and studied theoretically in more detail by Elander & Smith (1973), Brooks & Smith (1974), Elander et al (1979), andvan Dishoeck (1987). For the A state, Brzozowski et al (1976) noticed that the line structure disappears for energies below the dissociation limit, but reappears again at higher energies.…”

Section: A1 Predissociation Lines In Astronomical Spectramentioning

confidence: 71%

CH in stellar atmospheres: an extensive linelist

Masseron

Plez

Eck

et al. 2014

A&A

242

216

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The advent of high-resolution spectrographs and detailed stellar atmosphere modelling has strengthened the need for accurate molecular data. Carbon-enhanced metal-poor (CEMP) stars spectra are interesting objects with which to study transitions from the CH molecule. We combine programs for spectral analysis of molecules and stellar-radiative transfer codes to build an extensive CH linelist, including predissociation broadening as well as newly identified levels. We show examples of strong predissociation CH lines in CEMP stars, and we stress the important role played by the CH features in the Bond-Neff feature depressing the spectra of barium stars by as much as 0.2 mag in the λ = 3000−5500 Å range. Because of the extreme thermodynamic conditions prevailing in stellar atmospheres (compared to the laboratory), molecular transitions with high energy levels can be observed. Stellar spectra can thus be used to constrain and improve molecular data.

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“…The measured equivalent widths of the lines arising in the C-X system are converted into column densities using the molecular parameters and the method of Lien (1984). For the oscillator strength of the (1, 0) band of the B-X system, we scale the value of the (0, 0) band of Lien (1984) using the ratio of 7.8 of the band oscillator strengths of the (0, 0) and (1, 0) bands as inferred from the lifetime measurements of Brooks & Smith (1974). The observed CH absorption lines and line blends arise from the lower or upper component of the J = 1/2 Λ-doublet.…”

Section: Detected Thementioning

confidence: 99%

Abundances of PAHs in the ISM: confronting observations with experimental results

Gredel

Carpentier

Rouillé

et al. 2011

A&A

104

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Context. The identification of the carriers of the diffuse interstellar bands (DIBs) is the longest standing problem in the study of the interstellar medium. Here we present recent UV laboratory spectra of various polycyclic aromatic hydrocarbons (PAHs) and explore the potential of these molecules as carriers of the DIBs. Whereas, in the near IR range, the PAHs exhibit vibrational bands that are not molecule-specific, their electronic transitions occurring in the UV/vis provide characteristic fingerprints. The comparison of laboratory spectra calibrated in intensity with high signal-to-noise observational data in the UV enables us to establish new constraints on PAH abundances. Aims. From a detailed comparison of the gas-phase and Ne-matrix absorption spectra of anthracene, phenanthrene, pyrene, 2,3-benzofluorene, benzo[ghi]perylene, and hexabenzocoronene with new interstellar spectra, we aim to infer the abundance of these PAHs in the interstellar medium. Methods. We present spectra of PAHs measured at low temperature in the gas phase and in an Ne matrix, and present methods to derive absolute absorption cross sections for the matrix and gas phase spectra. We have obtained high signal to noise (S/N > 100) absorption spectra toward five lines of sight with reddenings of E B−V = 1−1.6 mag. The spectra cover the 3050−3850 Å wavelength region where the PAHs studied here show prominent absorption features. Results. From the observations, we infer upper limits in the fractional abundances of the PAHs studied here. Upper limits in the column densities of anthracene of 0.8−2.8 × 10 12 cm −2 and of pyrene and 2,3-benzofluorene ranging from 2−8 × 10 12 cm −2 are inferred. Upper limits in the column densities of benzo [ghi]perylene are 0.9−2.4 × 10 13 and 10 14 cm −2 for phenanthrene. The measurements indicate fractional abundances of anthracene, pyrene, and 2,3-benzofluorene of a few times 10 −10 . Upper limits in the fractional abundance of benzo [ghi]perylene of a few times 10 −9 and of phenanthrene of few times 10 −8 are inferred. Toward CPD −32 • 1734, we found near 3584 Å an absorption line of OH + , which was discovered in the interstellar medium only very recently. Conclusions. The fractional abundances of PAHs inferred here are up to two orders of magnitude lower than estimated total PAH abundances in the interstellar medium. This indicates that either neutral PAHs are not abundant in translucent molecular clouds or that a PAH population with a wide variety of molecules is present.

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Radiative and predissociation probabilities for individual rotational levels of the B 2Sigma state of CH with application to the radiative recombination of CH in the interstellar medium

Cited by 21 publications

References 0 publications

High-Resolution Spectroscopy of the A-X and B-X System of CH in Comet Austin (1990 V).

High-Resolution Spectroscopy of the A-X and B-X System of CH in Comet Austin (1990 V).

CH in stellar atmospheres: an extensive linelist

Abundances of PAHs in the ISM: confronting observations with experimental results

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