Ab initio studies of the photodissociation processes in positive hydrocarbon ions. I. The methane ion

Dishoeck, E. F. van; Hart, W.J. van der; Hemert, M. van

doi:10.1016/0301-0104(80)87024-8

Cited by 49 publications

(13 citation statements)

References 28 publications

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“…In C 3 v symmetry, the (2a 1 ) −1 state of CH 4 + is correlated with the first H + + CH 3 dissociation limit [27], which is located 18.1 eV above the methane ground state. Thus, there is an excess energy of at least 4.2 eV compared to the vertical ionization energy of the (2a 1 ) −1 state that has to be taken away by the fragments.…”

Section: Resultsmentioning

confidence: 96%

Formation of protons from dissociative ionization of methane induced by 54 eV electrons

Ren

et al. 2011

Phys. Rev. A

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The production mechanisms of protons in dissociation of methane by 54 eV electron impact is investigated using the reaction microscope. By measuring all three charged particles in the final state in triple coincidence, the energy deposited in the target is determined. It is found that the (2a 1 ) −1 (npt 2 ) 1 , (2a 1 ) −1 , (1t 2 ) −2 (3a 1 ) 1 , and (2a 1 ) −2 (3a 1 ) 1 states of the intermediate CH 4 + make the major contributions to the formation of protons at this incident energy. The decay of each state results in a different kinetic energy distribution of protons. Possible decay mechanisms of these states are analyzed.

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Section: Resultsmentioning

confidence: 96%

Formation of protons from dissociative ionization of methane induced by 54 eV electrons

Ren

et al. 2011

Phys. Rev. A

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“…This ion is subject to detailed theoretical studies indicating several dissociative excited states (van Dishoeck et al 1980). Oscillator strengths into the 2, 3 2 A 1 and 2 2 B 1 states are taken to be f = 0.04, 0.04 and 0.08, respectively, with η d = 1.…”

Section: Ch + 4 -Methane Cationmentioning

confidence: 99%

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

Heays

Bosman

Dishoeck

2017

A&A

428

442

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A new collection of photodissociation and photoionisation cross sections for 102 atoms and molecules of astrochemical interest has been assembled, along with a brief review of the basic physical processes involved. These have been used to calculate dissociation and ionisation rates, with uncertainties, in a standard ultraviolet interstellar radiation field (ISRF) and for other wavelength-dependent radiation fields, including cool stellar and solar radiation, Lyman-α dominated radiation, and a cosmic-ray induced ultraviolet flux. The new ISRF rates generally agree within 30% with our previous compilations, with a few notable exceptions. Comparison with other databases such as PHIDRATES is made. The reduction of rates in shielded regions was calculated as a function of dust, molecular and atomic hydrogen, atomic C, and self-shielding column densities. The relative importance of these shielding types depends on the atom or molecule in question and the assumed dust optical properties. All of the new data are publicly available from the Leiden photodissociation and ionisation database. Sensitivity of the calculated rates to variation of temperature and isotope, and uncertainties in measured or calculated cross sections, are tested and discussed. Tests were conducted on the new rates with an interstellar-cloud chemical model, and find general agreement (within a factor of two) in abundances obtained with the previous iteration of the Leiden database assuming an ISRF, and order-of-magnitude variations assuming various kinds of stellar radiation. The newly parameterised dust-shielding factors makes a factor-of-two difference to many atomic and molecular abundances relative to parameters currently in the UDfA and KIDA astrochemical reaction databases. The newly-calculated cosmic-ray induced photodissociation and ionisation rates differ from current standard values up to a factor of 5. Under high temperature and cosmic-ray-flux conditions the new rates alter the equilibrium abundances of abundant dark cloud abundances by up to a factor of two. The partial cross sections for H 2 O and NH 3 photodissociation forming OH, O, NH 2 and NH are also evaluated and lead to radiation-field-dependent branching ratios.

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“…The second calculation, made with the Wuppertal-Bonn MRD-CI package of programs (Buenker et al 1978;van Dishoeck et al 1980) used a Gaussian basis. All single and double excitation configurations with respect to the most important (c i 0:1) species, 52 about ten in number, in the CI expansion were generated, keeping the 1 orbital doubly occupied.…”

Section: Photodissociationmentioning

confidence: 99%

Opacity

Huebner

Barfield

2014

Astrophysics and Space Science Library

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Ab initio studies of the photodissociation processes in positive hydrocarbon ions. I. The methane ion

Cited by 49 publications

References 28 publications

Formation of protons from dissociative ionization of methane induced by 54 eV electrons

Formation of protons from dissociative ionization of methane induced by 54 eV electrons

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

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