Deuterium fractionation in dense interstellar clouds

Millar, T. J.; Bennett, Alec; Herbst, Eric

doi:10.1086/167444

Cited by 393 publications

(350 citation statements)

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“…Concerning isotope fractionation under interstellar conditions, these activities slowed down about 20 years ago, and there are almost no recent experiments performed with merged beams or ow techniques on this subject. Excluding the present work, it seems to be correct to assume that the review by Millar et al (1989) contains most of the experimental information on deuteration. In the following the situation will be illustrated for three collision systems.…”

Section: Resultsmentioning

confidence: 83%

“…3 where the theory is also rather good; however, one should be aware that erroneous conclusions can be made if one extrapolates the temperature trends of a few points towards lower temperatures. This can be seen from a comparison of the numerical values given in Table 2 and also Only reference to MBH89 (Millar et al, 1989) is given which is a compilation of the relevant data with further references. GHR02 refers to Gerlich et al (2002) in this volume.…”

Section: + + Hmentioning

confidence: 99%

“…Its role in interstellar ion chemistry, especially for deuterating other molecules, has been discussed thoroughly in the literature (Millar et al, 1989;Millar, 2002). It is formed via the classic proton transfer reaction…”

Section: + 3 + Hmentioning

confidence: 99%

“…In order to correlate quantitatively XD/XH ratios with parameters such as (i) D / H isotope ratio, (ii) ambient temperatures, and (iii) density of atoms, molecules, and electrons, one has to know in detail the kinetics and dynamics of a variety of processes including chemical reactions, inelastic collisions and radiative transitions. The reactions and parameters used in present gas-phase chemistry models lead to the conclusion that deuterium fractionation is dominated by the molecules HD; H 2 D + ; CH 2 D + ; C 2 HD + the abundance ratio of which, XD/XH, is much larger than the elemental ratio of typically D=H = 2 × 10 −5 (Millar et al, 1989). In recent years, the activities of interstellar grains in isotope exchange and enrichment have also been accounted for (Millar, 2002).…”

Section: Introductionmentioning

confidence: 99%

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Deuterium fractionation in gas-phase reactions measured in the laboratory

Gerlich

2002

Planetary and Space Science

108

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In order to understand quantitatively the enrichment of deuterated molecules observed in non-equilibrium environments such as interstellar clouds, one has to know in detail many state-to-state cross sections. For detailed models, one has to treat both chemical processes such as formation and destruction of the isotopomers and physical processes such as collisional excitation and radiative transitions of the relevant molecular states. This contribution gives a short summary of experimental techniques in the ÿeld of low-energy gas-phase collisions such as ow techniques, traps, and beam methods with special emphasis on those methods which can be used to study the dynamics of H-D scrambling. The situation is illustrated with the astrophysically important H + + H2 collision system in several isotopic variants. This fundamental system is well understood, and most experimental results are in good accordance with predictions from a dynamically biased statistical model. Less well understood are the di erent isotopic combinations of H + 3 colliding with H2. The H + 3 + HD variant is discussed in a separate paper in this special issue (H + 3 + HD ↔ H2D + + H2:low-temperature laboratory measurements and interstellar implications, Planet. Space Sci., this volume) while, in this contribution, the situation is illustrated with rate coe cients for isotopic exchange in D + 3 + H2 collisions. Other examples include the study of deuteration of hydrocarbon ions in a trap at a nominal temperature of 10 K. In particular, the rate coe cients for sequential deuteration of C2H + 2 in collisions with HD have been measured to be 7:5×10 −10 cm 3 s −1 and 7:0 × 10 −10 cm 3 s −1 . Another example refers to the reactions that occur when CH + 3 is stored in para-hydrogen (p-H2) or normal-hydrogen (n-H2) containing the natural abundance of HD. At the low densities used, H-D exchange competes only with radiative association. Some hints to the next generation of experiments are given. One of the aims is to study the role of H atoms and D atoms in low-temperature gas-phase chemistry. Another aim is to combine laser and trapping techniques in order to get both state speciÿc rate coe cients and spectroscopic information. ?

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Section: Resultsmentioning

confidence: 83%

Section: + + Hmentioning

confidence: 99%

Section: + 3 + Hmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Deuterium fractionation in gas-phase reactions measured in the laboratory

Gerlich

2002

Planetary and Space Science

108

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“…The most relevant case for star-forming regions is the deuterium fractionation, initiated by the isotope exchange reactions H + 3 + HD → H 2 D + + H 2 and CH + 3 + HD → CH 2 D + + H 2 (Wootten 1987, Millar et al 1989. These reactions occur preferentially in the forward direction at low temperatures, because the heavier H 2 D + and CH 2 D + are slightly more stable than H + 3 and CH + 3 due to their lower zero-point vibrational energy.…”

Section: Fractionationmentioning

confidence: 99%