Interstellar Complex Organic Molecules and the Minimum Energy Principle

Lattelais, M.; Pauzat, F.; Ellinger, Y.; Ceccarelli, C.

doi:10.1088/0004-637x/696/2/l133

Cited by 100 publications

(139 citation statements)

References 40 publications

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“…In addition, the abundance ratio of the most stable isomer to the other isomers seemed to be directly related to their energy difference. What can be regarded as a minimum energy principle (MEP) (Lattelais et al 2009), is verified in molecular clouds, hot cores/corinos, photodissociation regions, and asymptotic giant branch stars. We have proposed that the few exceptions encountered could be rationalized either by the existence of different routes of formation with no intermediate processes in common and/or have a special type of depletion on the grains of one isomer with respect to the others.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 96%

“…The contradiction with the MEP comes from the relative stabilities of these isomers. High level ab-initio coupled cluster calculations with large correlation consistent basis sets 3 have shown (Lattelais et al 2009) that acetic acid is more stable than methyl formate by ∼17 kcal mol −1 and ethanol more stable than di-methyl ether by ∼12 kcal mol −1 .…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

“…As a consequence, any modelling of grain surfaces is also a matter of discussion and the theoretical results have to be confronted with laboratory experiments about interstellar ice analogues in conditions as close as possible to the interstellar environment. It is this joint research that is presented in the following pages, from the initial theoretical work to the final experimental confirmation, focused on the adsorption of two couples of isomers, namely: acetic acid A&A 532, A12 (2011) (AA)/methyl formate (MF) and ethanol (EtOH)/di-methyl ether (DME) that appeared as exceptions to the minimum energy principle(MEP) (Lattelais et al 2009). …”

Section: Introductionmentioning

confidence: 99%

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Differential adsorption of complex organic molecules isomers at interstellar ice surfaces

Lattelais

Bertin

Mokrane

et al. 2011

A&A

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Context. Over 20 of the ∼150 different species detected in the interstellar and circumstellar media have also been identified in icy environments. For most of the species observed so far in the interstellar medium (ISM), the most abundant isomer of a given generic chemical formula is the most stable one (minimum energy principle -MEP) with few exceptions such as, for example, CH 3 COOH/HCOOCH 3 and CH 3 CH 2 OH/CH 3 OCH 3 , whose formation is thought to occur on the icy mantles of interstellar grains. Aims. We investigate whether differences found in the compositions of molecular ices and the surrounding gas phase could originate from differences between the adsorption of one isomer from that of another at the ice surface. Methods. We performed a coherent and concerted theoretical/experimental study of the adsorption energies of the four molecules mentioned above, i.e. acetic acid (AA)/methyl formate (MF) and ethanol (EtOH)/dimethyl ether (DME) on the surface of water ice at low temperature. The question was first addressed theoretically at LCT using solid state periodic density functional theory (DFT) to represent the organized solid support. The experimental determination of the ice/molecule interaction energies was then carried out independently by two teams at LPMAA and LERMA/LAMAp using temperature programmed desorption (TPD) under an ultra-high vacuum (UHV) between 70 and 160 K. Results. For each pair of isomers, theory and experiments both agree that the most stable isomer (AA or EtOH) interacts more efficiently with the water ice than the higher energy isomer (MF or DME). This differential adsorption can be clearly seen in the different desorption temperatures of the isomers. It is not related to their intrinsic stability but instead to both AA and EtOH producing more and stronger hydrogen bonds with the ice surface. Conclusions. We show that hydrogen bonding may play an important role in the release of organic species from grains and propose that, depending on the environment, differential adsorption should not be rejected as a possible way of interpreting MEP exceptions.

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Section: Discussion and Concluding Remarksmentioning

confidence: 96%

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Differential adsorption of complex organic molecules isomers at interstellar ice surfaces

Lattelais

Bertin

Mokrane

et al. 2011

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“…To this end, we use the results of Lattelais et al (2009). Briefly, based on the observations towards astronomical sources available in the literature and new computations of the stability of the isomers of same generic chemical formula, it has been found that the most abundant isomers of the same chemical formula are the most stable, with only two exceptions over a sample of 32 isomeric forms.…”

Section: Introductionmentioning

confidence: 99%

About the detectability of glycine in the interstellar medium

Lattelais

Pauzat

Pilmé

et al. 2011

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Context. Glycine, the simplest of aminoacids, has been found in several carbonaceous meteorites. It remains unclear, however, wether glycine is formed in the interstellar medium (ISM) and therefore available everywhere in the Universe. For this reason, radioastronomers have searched for many years unsuccessfully to detect glycine in the ISM. Aims. We provide possible guidelines to optimize the return of these searches. Since, for most of the species observed so far in the ISM, the most abundant isomer of a given generic chemical formula is the most stable one (minimum energy principle (MEP)), we assess whether neutral glycine is the best molecule to search for or whether one of its isomers/conformers or ionic, protonated, or zwitterionic derivatives would have a higher probability of being detected. Methods. The question of the relative stability of these different species is addressed by means of quantum density functional theory (DFT) simulations within the hybrid B3LYP formalism. Each fully optimized structure is verified as a stationary point by means of a vibrational analysis. A comprehensive screening of 32 isomers/conformers of the C 2 H 5 O 2 N chemical formula (neutral, negative, and positive ions together with the corresponding protonated species and the possible zwitterionic structures) is carried out. In the sensitive case of the neutral compounds, more accurate relative energies were obtained by means of high level post Hartree-Fock coupled cluster calculations with large basis sets (CCSD(T)/cc-pVQZ). Results. We find that neutral glycine is not the most stable isomer and, therefore, probably not the most abundant one, which might explain why it has escaped detection so far. We find instead that N-methyl carbamic acid and methyl carbamate are the two most stable isomers and, therefore, probably the two most abundant ones. Among the non-neutral forms, we found that glycine is the most stable isomer only if protonated or zwitterionic if present in interstellar ices. Conclusions. Assuming that MEP can be applied to optimize our search for glycine, our conclusion is that this search will remain extremely difficult with the present instruments and we propose searching instead for other examples among the most stable isomers.

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“…Unsuccessful attempts to discover a first chiral compound in the ISM have already been reported, and propylene epoxyde (H 2 C(O)CHCH 3 ) was the target Cunningham et al 2007). Many other chiral compounds could be present in the ISM with substituents largely represented in the list of detected molecules (Marloie et al 2010;Lattelais et al 2009). Some of them are potential precursors of these building blocks of life.…”

Section: Introductionmentioning

confidence: 99%

Rotational spectrum of a chiral amino acid precursor, 2-aminopropionitrile, and searches for it in Sagittarius B2(N)

Møllendal

Margulès

Беллоче

et al. 2012

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Context. No chiral molecule has been detected in the interstellar medium (ISM) so far. Aims. A good candidate for an interstellar detection is 2-aminopropionitrile (CH 3 CH(NH 2 )CN), a chiral molecule with a C 3 H 6 N 2 formula. The first member of this series, aminoacetonitrile (H 2 NCH 2 CN), was recently detected, demonstrating that at least one aminonitrile exists in the ISM. Methods. Experimental spectra of 2-aminopropionitrile have been recorded in the microwave and submm energy range . Ab initio calculations facilitated the assignment of the ground state of the most stable conformer and its five lowest excited vibrational states. An unbiased spectral survey of the 80-116 GHz atmospheric window performed with the IRAM 30 m telescope was used to search for this molecule in the hot core Sgr B2(N). This survey was analyzed in the local thermodynamical equilibrium (LTE) approximation. The emission of 2-aminopropionitrile was modeled simultaneously with the emission of all molecules known in Sgr B2(N), which allowed us to properly take into account line blending and avoid misassignments. Results. More than 4000 lines of the ground state and the five lowest excited vibrational states (from 185 to 375 cm −1 ) were assigned in the experimental spectrum. The partition function including the vibrational contribution of these states was calculated. Only ten groups of transitions of 2-aminopropionitrile are not severely affected by line blending in the Sgr B2(N) spectrum. Six of them could be considered as tentatively detected but the LTE predictions of the four remaining groups are not (or only marginally) consistent with the observed spectrum. Therefore, only an upper limit of 1.7 × 10 16 cm −2 can be securely derived for the column density of 2-aminopropionitrile toward Sgr B2(N), assuming the same source size, temperature, linewidth, and systemic velocity as for aminoacetonitrile Conclusions. 2-aminopropionitrile is at least 1.8 times less abundant than aminoacetonitrile. A simple comparison to the pair methyl cyanide (CH 3 CN)/ethyl cyanide (CH 3 CH 2 CN) detected toward Sgr B2(N) suggests that 2-aminopropionitrile should be 3.5 times less abundant than aminoacetonitrile, which is consistent with the limit derived here.

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Interstellar Complex Organic Molecules and the Minimum Energy Principle

Cited by 100 publications

References 40 publications

Differential adsorption of complex organic molecules isomers at interstellar ice surfaces

Differential adsorption of complex organic molecules isomers at interstellar ice surfaces

About the detectability of glycine in the interstellar medium

Rotational spectrum of a chiral amino acid precursor, 2-aminopropionitrile, and searches for it in Sagittarius B2(N)

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