The Comet-Tail (A2Πi–X2Σ+) System of 12C16O+: A Reinvestigation

Aims. Photodissociation by UV light is an important destruction mechanism for carbon monoxide (CO) in many astrophysical environments, ranging from interstellar clouds to protoplanetary disks. The aim of this work is to gain a better understanding of the depth dependence and isotope-selective nature of this process.Methods. We present a photodissociation model based on recent spectroscopic data from the literature, which allows us to compute depth-dependent and isotope-selective photodissociation rates at higher accuracy than in previous work. The model includes self-shielding, mutual shielding and shielding by atomic and molecular hydrogen, and it is the first such model to include the rare isotopologues C 17 O and 13 C 17 O. We couple it to a simple chemical network to analyse CO abundances in diffuse and translucent clouds, photon-dominated regions, and circumstellar disks. Results. The photodissociation rate in the unattenuated interstellar radiation field is 2.6 × 10 −10 s −1 , 30% higher than currently adopted values. Increasing the excitation temperature or the Doppler width can reduce the photodissociation rates and the isotopic selectivity by as much as a factor of three for temperatures above 100 K. The model reproduces column densities observed towards diffuse clouds and PDRs, and it offers an explanation for both the enhanced and the reduced N( 12 CO)/N( 13 CO) ratios seen in diffuse clouds.

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“…c ω e and ω e x e from the CO ground state (Guelachvili et al 1983 (Haridass et al 2000). ω e y e (not listed) is included in the model.…”

Section: Band Positions and Identificationsmentioning

confidence: 99%

“…27), we can derive ω e from the difference in ν 0 ; • else, if it is part of a Rydberg series converging to the X 2 Σ + or A 2 Π state of CO + , we take those constants (Haridass et al 2000);…”

Section: Band Positions and Identificationsmentioning

confidence: 99%

The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks

Visser

Dishoeck

Black

2009

A&A

527

688

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“…The corresponding constants necessary for the above calculations have been obtained by isotopic recalculating of equilibrium molecular contants of the A (11,20) and X (11,25) states obtained earlier for the 12 C 16 O + molecule. The final analysis and the calculation of constants were performed in many stages via a nonlinear least-squares procedure and by means of effective Hamiltonians proposed by Brown et al (26).…”

Section: Calculation Of Constantsmentioning

confidence: 99%

“…The bibliography and tabulations of the spectroscopic information dealing with the four electronic states, X 2 + , A The comet-tail system, being one of the most comprehensive band systems of this molecule, has been explored the most extensively in the most abundant isotopomer 12 C 16 O + (1,(4)(5)(6)(7)(8)(9)(10)(11). There have been fewer works, which were concerned with a smaller number of bands, devoted to the study of this system in the other isotopomers of CO + .…”

Section: Introductionmentioning

confidence: 99%

Analysis of the Comet-Tail (A2Π –X2Σ+) Bands of 13C16O+

Kępa

Kocan

Ostrowska

et al. 2002

Journal of Molecular Spectroscopy

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“…As a result, they received a unique set of molecular constants for the X, A, and B states. In 2000, these authors carried out a corrective analysis of 10 bands of the A-X system earlier investigated by them and obtained a new set of constants for the X and A states [22]. In 2001, Zhuang et al [23] recorded the 1-2 and 2-3 bands by means of the optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy method.…”

Section: Introductionmentioning

confidence: 98%