Our astrochemical heritage

Caselli, P.; Ceccarelli, C.

doi:10.1007/s00159-012-0056-x

Cited by 428 publications

(442 citation statements)

References 452 publications

Supporting

Mentioning

433

Contrasting

Unclassified

Order By: Relevance

“…The present study is also the first report to our knowledge of the nonenergetic deuteration of aromatic hydrocarbons at low temperature. We discuss the importance of our findings for astrochemistry and geochemistry in relation to the origin of deuterium enrichment observed in extraterrestrial materials such as interstellar aromatic/aliphatic hydrocarbons, carbonaceous meteorites, and interplanetary dust particles (12)(13)(14)(15)(16)(17), the chemistry of which influences our understanding of interstellar physicochemical processes, including the formation of the solar system (18)(19)(20). .…”

Section: Significancementioning

confidence: 91%

Quantum tunneling observed without its characteristic large kinetic isotope effects

Hama

Ueta

Kouchi

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Classical transition-state theory is fundamental to describing chemical kinetics; however, quantum tunneling is also important in explaining the unexpectedly large reaction efficiencies observed in many chemical systems. Tunneling is often indicated by anomalously large kinetic isotope effects (KIEs), because a particle's ability to tunnel decreases significantly with its increasing mass. Here we experimentally demonstrate that cold hydrogen (H) and deuterium (D) atoms can add to solid benzene by tunneling; however, the observed H/D KIE was very small (1-1.5) despite the large intrinsic H/D KIE of tunneling (≳100). This strong reduction is due to the chemical kinetics being controlled not by tunneling but by the surface diffusion of the H/D atoms, a process not greatly affected by the isotope type. Because tunneling need not be accompanied by a large KIE in surface and interfacial chemical systems, it might be overlooked in other systems such as aerosols or enzymes. Our results suggest that surface tunneling reactions on interstellar dust may contribute to the deuteration of interstellar aromatic and aliphatic hydrocarbons, which could represent a major source of the deuterium enrichment observed in carbonaceous meteorites and interplanetary dust particles. These findings could improve our understanding of interstellar physicochemical processes, including those during the formation of the solar system. quantum tunneling | kinetic isotope effect | heterogeneous reactions | reaction dynamics | astrochemistry

show abstract

Section: Significancementioning

confidence: 91%

Quantum tunneling observed without its characteristic large kinetic isotope effects

Hama

Ueta

Kouchi

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…The onset of the water ice mantle formation requires a threshold extinction, above which the photodesorption rate of water ice is lower than the formation rate of water ice Öberg et al 2011). On the other hand, the formation rates of HDO and D 2 O ices do not necessarily decrease together with that of H 2 O ice; deuterium fractionation is more efficient at later times, as CO is frozen out, the ortho-to-para nuclear spin ratio of H 2 (OPR(H 2 )) decreases, and interstellar UV radiation is heavily shielded (e.g., Caselli & Ceccarelli 2012, and references therein). Infrared observations show that H 2 O ice starts to become abundant in molecular clouds above a threshold line-of-sight visual extinction, depending on environments, e.g., ∼3 mag for Taurus dark clouds (Whittet 1993;Boogert et al 2015, and references therein).…”

Section: Scenariomentioning

confidence: 99%

Reconstructing the history of water ice formation from HDO/H₂O and D₂O/HDO ratios in protostellar cores

Furuya

Dishoeck

Aikawa

2016

A&A

137

View full text Add to dashboard Cite

Recent interferometer observations have found that the D 2 O/HDO abundance ratio is higher than that of HDO/H 2 O by about one order of magnitude in the vicinity of low-mass protostar NGC 1333-IRAS 2A, where water ice has sublimated. Previous laboratory and theoretical studies show that the D 2 O/HDO ice ratio should be lower than the HDO/H 2 O ice ratio, if HDO and D 2 O ices are formed simultaneously with H 2 O ice. In this work, we propose that the observed feature, D 2 O/HDO > HDO/H 2 O, is a natural consequence of chemical evolution in the early cold stages of low-mass star formation as follows: 1) majority of oxygen is locked up in water ice and other molecules in molecular clouds, where water deuteration is not efficient; and 2) water ice formation continues with much reduced efficiency in cold prestellar/protostellar cores, where deuteration processes are highly enhanced as a result of the drop of the ortho-para ratio of H 2 , the weaker UV radiation field, etc. Using a simple analytical model and gas-ice astrochemical simulations, which traces the evolution from the formation of molecular clouds to protostellar cores, we show that the proposed scenario can quantitatively explain the observed HDO/H 2 O and D 2 O/HDO ratios. We also find that the majority of HDO and D 2 O ices are likely formed in cold prestellar/protostellar cores rather than in molecular clouds, where the majority of H 2 O ice is formed. This work demonstrates the power of the combination of the HDO/H 2 O and D 2 O/HDO ratios as a tool to reveal the past history of water ice formation in the early cold stages of star formation, and when the enrichment of deuterium in the bulk of water occurred. Further observations are needed to explore if the relation, D 2 O/HDO > HDO/H 2 O, is common in low-mass protostellar sources.

show abstract

“…Specifically, hydrogenation of CO sequentially forms formaldehyde first and then methanol: thus, as time proceeds, the formation of methanol and their deuterated isotopologues is boosted, until the energy released by the nascent protostellar object in the form of radiation increases the temperature of its environment, causing the evaporation of the grain mantles and the release of these molecules into the gas. As the temperature increases and the protostar evolves towards the UC Hii region phase, the deuterated species are expected to be gradually destroyed because of the higher efficiency of the backward endothermic reactions (see Caselli & Ceccarelli 2012, for a review). The trends shown in Fig.…”

Section: Deuterated Fraction Of Methanolmentioning

confidence: 99%

Deuteration and evolution in the massive star formation process

Fontani

Busquet

Palau

et al. 2015

A&A

131

View full text Add to dashboard Cite

Context. An ever growing number of observational and theoretical evidence suggests that the deuterated fraction (column density ratio between a species containing D and its hydrogenated counterpart, D frac ) is an evolutionary indicator both in the low-and the highmass star formation process. However, the role of surface chemistry in these studies has not been quantified from an observational point of view. Aims. Because many abundant species, such as NH 3 , H 2 CO, and CH 3 OH, are actively produced on ice mantles of dust grains during the early cold phases, their D frac is expected to evolve differently from species formed only (or predominantly) in the gas, such as N 2 H + , HNC, HCN, and their deuterated isotopologues. The differences are expected to be relevant especially after the protostellar birth, in which the temperature rises, causing the evaporation of ice mantles. Methods. To compare how the deuterated fractions of species formed only in the gas and partially or uniquely on grain surfaces evolve with time, we observed rotational transitions of CH 3 OH, 13 CH 3 OH, CH 2 DOH, and CH 3 OD at 3 mm and 1.3 mm, of NH 2 D at 3 mm with the IRAM-30 m telescope, and the inversion transitions (1, 1) and (2, 2) of NH 3 with the GBT, towards most of the cores already observed in N 2 H + , N 2 D + , HNC, and DNC. Results. NH 2 D is detected in all but two cores, regardless of the evolutionary stage. D frac (NH 3 ) is on average above 0.1 and does not change significantly from the earliest to the most evolved phases, although the highest average value is found in the protostellar phase (∼0.3). Few lines of CH 2 DOH and CH 3 OD are clearly detected, and then only towards protostellar cores or externally heated starless cores. In quiescent starless cores, we have only one doubtful detection of CH 2 DOH. Conclusions. This work clearly confirms an expected different evolutionary trend of the species formed exclusively in the gas (N 2 D + and N 2 H + ) and those formed partially (NH 2 D and NH 3 ) or totally (CH 2 DOH and CH 3 OH) on grain mantles. It also reinforces the idea that D frac (N 2 H + ) is the best tracer of massive starless cores, while high values of D frac (CH 3 OH) seem fairly good tracers of the early protostellar phases, where the evaporation or sputtering of the grain mantles is most efficient.

show abstract

Our astrochemical heritage

Cited by 428 publications

References 452 publications

Quantum tunneling observed without its characteristic large kinetic isotope effects

Quantum tunneling observed without its characteristic large kinetic isotope effects

Reconstructing the history of water ice formation from HDO/H₂O and D₂O/HDO ratios in protostellar cores

Deuteration and evolution in the massive star formation process

Contact Info

Product

Resources

About

Our astrochemical heritage

Cited by 428 publications

References 452 publications

Quantum tunneling observed without its characteristic large kinetic isotope effects

Quantum tunneling observed without its characteristic large kinetic isotope effects

Reconstructing the history of water ice formation from HDO/H2O and D2O/HDO ratios in protostellar cores

Deuteration and evolution in the massive star formation process

Contact Info

Product

Resources

About

Reconstructing the history of water ice formation from HDO/H₂O and D₂O/HDO ratios in protostellar cores