The rotational excitation of methanol by helium at low temperatures

Pottage, J T; Flower, D. R.; Davis, Stephen L.

doi:10.1088/0953-4075/34/16/309

Cited by 20 publications

(34 citation statements)

References 18 publications

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“…The results show that the rate coefficients decrease with increasing ∆ j. This propensity is the usual trend and was found for other systems like CH 3 OH-He (Pottage et al 2001).…”

Section: Resultssupporting

confidence: 77%

“…This approximation has been used for complex collisional systems, such as He in collision with H 2 CO (Green et al 1978), CH 3 CN (Green 1985), CH 3 OH (Pottage et al 2001), H 2 in collision with H 2 O (Phillips et al 1995). The present calculations were performed with the MOLSCAT code of Hutson & Green (1995) in the atomasymmetric top CS approximation and with the log-derivative method of Manolopoulos (1986).…”

Section: Dynamics Of Hoco + -He Collisionsmentioning

confidence: 99%

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Rotational excitation of HOCO⁺ by helium at low temperature

Hammami

Lique

Jaı̈dane

et al. 2006

A&A

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Context. It has been shown that the HOCO+ ion is present in interstellar space. As a large number of HOCO + lines can be observed in the millimeter and submillimeter wavelengths, this molecule is a useful tracer for both the temperature and the density structure of the clouds. Modeling of the spectra will require accurate radiative and collisional rates of species of astrophysical interest. Aims. The paper focuses on the calculation of rotational excitation rate coefficients of HOCO + by He, useful for studies of lowtemperature environments. Methods. Cross sections are calculated using the quantum Coupled States approach for a total energy range 0-200 cm −1 . These calculations are based on a new ab initio CEPA (coupled electron pair approach) potential energy surface. It was assumed that the HOCO + ion was fixed at its theoretical equilibrium geometry. Results. Thermally averaged rate coefficients were calculated from the cross sections, at kinetic temperatures up to 30 K.

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“…The results show that the rate coefficients decrease with increasing ∆ j. This propensity is the usual trend and was found for other systems like CH 3 OH-He (Pottage et al 2001).…”

Section: Resultssupporting

confidence: 77%

Section: Dynamics Of Hoco + -He Collisionsmentioning

confidence: 99%

Rotational excitation of HOCO⁺ by helium at low temperature

Hammami

Lique

Jaı̈dane

et al. 2006

A&A

View full text Add to dashboard Cite

show abstract

“…2, are compatible with the electric dipole selection rules. The small values of the rate coefficients for transitions with Δ j = 0 have been remarked upon previously by Pottage, Flower & Davis (2001, hereafter PFD01). It is attributable to the fact that Δ j = 0 corresponds, by definition, to inter‐ladder transitions, whose rate coefficients are smaller than those for intra‐ladder transitions, in which |Δ j | > 0.…”

Section: Resultssupporting

confidence: 65%

The rotational excitation of methanol by molecular hydrogen

Rabli

Flower

2010

Monthly Notices of the Royal Astronomical Society

142

123

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We have computed cross‐sections and rate coefficients for the rotational excitation of A‐ and E‐type methanol by molecular hydrogen. Calculations were performed for rotational transitions within the torsional ground state, ν= 0, and within the first and second excited torsional states, ν= 1 and ν= 2. For collisions of methanol with para‐H2 in its rotational ground state, j2= 0, the methanol basis included rotational states j1≤ 15, thereby extending previous calculations, which included states j1≤ 9 only. For the first time, calculations have also been performed for ortho‐H2 in its rotational ground state, j2= 1, although it was necessary to revert to the smaller methanol basis, j1≤ 9, owing to the coupling to states of molecular hydrogen with j2 > 0. The coupled states approximation was used in the production calculations, to generate the thermal rate coefficients at temperatures 10 ≤T≤ 200 K, but some limited comparisons, at a few collision energies, of cross‐sections obtained using the full coupled channels (CC) method have been made. The propensities of the collisions, with respect to changes in the rotational quantum number, j1, and its projection, K, on the symmetry axis of the methanol molecule, were investigated. There are qualitative differences between the K propensities for collisions with ortho‐ and para‐H2, which relate to the fact that the inelastic cross‐sections tend to be significantly larger when ortho‐H2 is the perturber.

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“…An LVG source code for methanol (CH 3 OH) was kindly provided by S. Leurini. Einstein coefficients were taken from Cragg et al (1993), energy levels were adopted from Xu & Lovas (1997), and collision rates are from Pottage et al (2001Pottage et al ( , 2002 for T kin ∼ 20 K and from D. Flower (priv. comm.)…”

Section: Ch 3 Ohmentioning

confidence: 99%

Dense gas in nearby galaxies

Wang

Henkel²,

Chin

et al. 2004

A&A

129

184

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Abstract.A multi-line millimeter-wave study of the nearby starburst galaxy NGC 4945 has been carried out using the Swedish-ESO Submillimeter Telescope (SEST). The study covers the frequency range from 82 GHz to 354 GHz and includes 80 transitions of 19 molecules. 1.3 mm continuum data of the nuclear source are also presented. An analysis of CO and 1.3 mm continuum fluxes indicates that the conversion factor between H 2 column density and CO J = 1−0 integrated intensity is smaller than in the galactic disk by factors of 5−10. A large number of molecular species indicate the presence of a prominent high density interstellar gas component characterized by n H 2 ∼ 10 5 cm −3 . Some spectra show Gaussian profiles. Others exhibit two main velocity components, one at ∼450 km s −1 , the other at ∼710 km s −1 . While the gas in the former component has a higher linewidth, the latter component arises from gas that is more highly excited as is indicated by HCN, HCO + and CN spectra. Abundances of molecular species are calculated and compared with abundances observed toward the starburst galaxies NGC 253 and M 82 and galactic sources. Apparent is an "overabundance" of HNC in the nuclear environment of NGC 4945. While the HNC/HCN J = 1−0 line intensity ratio is ∼0.5, the HNC/HCN abundance ratio is ∼1. From a comparison of K a = 0 and 1 HNCO line intensities, an upper limit to the background radiation of 30 K is derived. While HCN is subthermally excited (T ex ∼ 8 K), CN is even less excited (T ex ∼ 3−4 K), indicating that it arises from a less dense gas component and that its N = 2−1 line can be optically thin even though its N = 1−0 emission is moderately optically thick. Overall, fractional abundances of NGC 4945 suggest that the starburst has reached a stage of evolution that is intermediate between those observed in NGC 253 and M 82. Carbon, nitrogen, oxygen and sulfur isotope ratios are also determined. Within the limits of uncertainty, carbon and oxygen isotope ratios appear to be the same in the nuclear regions of NGC 4945 and NGC 253. S ratios (6.4 ± 0.3, 195 ± 45, 105 ± 25 and 13.5 ± 2.5 in NGC 4945, respectively) appear to be characteristic properties of a starburst environment in which massive stars have had sufficient time to affect the isotopic composition of the surrounding interstellar medium.

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The rotational excitation of methanol by helium at low temperatures

Cited by 20 publications

References 18 publications

Rotational excitation of HOCO⁺ by helium at low temperature

Rotational excitation of HOCO⁺ by helium at low temperature

The rotational excitation of methanol by molecular hydrogen

Dense gas in nearby galaxies

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The rotational excitation of methanol by helium at low temperatures

Cited by 20 publications

References 18 publications

Rotational excitation of HOCO+ by helium at low temperature

Rotational excitation of HOCO+ by helium at low temperature

The rotational excitation of methanol by molecular hydrogen

Dense gas in nearby galaxies

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Rotational excitation of HOCO⁺ by helium at low temperature

Rotational excitation of HOCO⁺ by helium at low temperature