Spectroscopic Parameters of HTiCN/HTiNC: New Titanium Compounds of Astrochemical Interest

Producción CientíficaA theoretical study of the [C, Ti, H, N] isomers, which are species of possible interstellar interest, has been carried out. We have employed different ab initio and density functional theory methodologies. Eleven isomers on the singlet, triplet, and quintet potential energy surfaces (PES) are characterized. The three most stable isomers of this system are obtained on the 3A″ PES from the interaction of the titanium atom of TiH with the cyano radical, CN, giving the open chains hydrotitanium cyanide/isocyanide (HTiCN/HTiNC) and the cyclic arrangement HTi-CN. For the most stable isomers we apply a composite approach that considers the extrapolation to the complete basis set limit, relativistic, and core-valence electron correlation corrections at the coupled-cluster level, including single and double excitations and a perturbative treatment of triple excitations (CCSD(T)). The lowest-lying isomer, HTiNC, is predicted to lie about 3.67 kcal mol−1 and 3.86 kcal mol−1 below HTiCN and the cyclic structure HTi-CN, respectively. The isomerization processes between these isomers shows that the cyclic structure could easily isomerize into HTiNC (the energy barrier is estimated to be only 0.48 kcal mol−1). We report harmonic and anharmonic frequencies, infrared intensities, and rotational constants that could help in their experimental characterization.Ministerio de Economía, Industria y Competitividad ( grant AYA2017-87515-P )Junta de Castilla y León (project VA010G18

Structure and Spectroscopic Properties of Hydrocalcium Isocyanide Isomers: Plausible Astronomical Ca-bearing Molecules

Producción CientíficaRecently, the first Ca-bearing molecule discovered in space, calcium isocyanide, CaNC, has been detected in the IRC+10216 circumstellar envelope. Related to CaNC are closed-shell stable molecules of [C, Ca, H, N] composition. One of the isomers with this composition is hydrocalcium isocyanide, HCaNC, which belongs to the hydrometal isocyanide/cyanide group of compounds, among which hydromagnesium isocyanide, HMgNC, is, to date, the only one detected in space. In this work, we have performed a study of the [C, Ca, H, N] isomers that are systems of possible interstellar interest by using quantum theoretical methodologies. The analysis of the relative energies predicts three low-lying isomers: c-HCa–NC (1A'), hydrocalcium isocyanide, HCaNC (1Σ), and hydrocalcium cyanide, HCaCN (1Σ). At the composite level, HCaNC (1Σ) and HCaCN (1Σ) were located 0.87 and 4.84 kcal mol−1, respectively, above the c-HCa–NC (1Σ) isomer. Interconversion processes between these isomers have been studied to analyze their stability. Isomer HCaNC is characterized as a transition state and thus directly isomerizes to the c-HCa–NC minimum. The isomerization process of HCaCN → c-HCa–NC shows a small barrier of about 0.76 kcal mol−1 (~382 K) above HCaCN, at the highest level of theory employed in this work, suggesting that HCaCN could easily isomerize into the most stable isomer, c-HCa–NC. Our results predict two low-lying isomers, namely, c-HCa–NC (1A') and hydrocalcium cyanide, HCaCN (1Σ), as possible candidates for experimental or radioastronomical detection. For these isomers, we provide predictions for their vibrational and rotational spectroscopic parameters that could aid in their eventual characterization in the laboratory or in space.Ministerio de Economía, Industria y Competitividad (grant AYA2017-87515-P)Junta de Castilla y León (grant VA010G18

Is the reaction between formic acid and protonated aminomethanol a possible source of glycine precursors in the interstellar medium?

Producción CientíficaContext. One of the most interesting questions in interstellar chemistry concerns whether we can detect the basic building blocks of proteins in astronomical sources. In ascertaining whether amino acids could be possible interstellar molecules, a crucial point is how they could be synthesized in the interstellar medium. Aims. We do a theoretical study of the ion-molecule reaction involving protonated aminomethanol and formic acid to establish its viability in space. This ion-molecule reaction has been proposed by other authors as a possible way to produce glycine in the interstellar medium. Methods. The relevant stationary points on the potential energy surface of the reaction between protonated aminomethanol and formic acid have been theoretically studied by using ab initio methods. The second-order Moller-Plesset level was employed, in conjunction with the correlation-consistent polarized valence triple-zeta (cc-pVTZ) basis set. In addition, the electronic energies were refined by means of single-point calculations at the CCSD(T) level (coupled cluster single and double excitation model augmented with a non-iterative treatment of triple excitations) on the MP2/cc-pVTZ geometries with the aug-cc-pVTZ basis set. Results. Formation of protonated glycine is an exothermic process; however, the process presents a net activation barrier that makes this reaction unfeasible under interstellar conditions. Conclusions. The reaction of protonated aminomethanol with formic acid does not seem to be a plausible source of interstellar glycine. This particular case is a clear example that a detailed study of the potential energy surface is needed to establish the relevance of a process in the interstellar medium.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13

Prediction of the Spectroscopic Parameters of New Iron Compounds: Hydride of Iron Cyanide/Isocyanide, HFeCN/HFeNC

Producción CientíficaIron is the most abundant transition metal in space. Its abundance is similar to that of magnesium, and until today only, FeO and FeCN have been detected. However, magnesium-bearing compounds such as MgCN, MgNC, and HMgNC are found in IRC+10216. It seems that the hydrides of iron cyanide/isocyanide could be good candidates to be present in space. In the present work we carried out a characterization of the different minima on the quintet and triplet [C, Fe, H, N] potential energy surfaces, employing several theoretical approaches. The most stable isomers are predicted to be hydride of iron cyanide HFeCN, and isocyanide HFeNC, in their 5 states. Both isomers are found to be quasi-isoenergetics. The HFeNC isomer is predicted to lie about 0.5 kcal/mol below HFeCN. The barrier for the interconversion process is estimated to be around 6.0 kcal/mol, making this process unfeasible under low temperature conditions, such as those in the interstellar medium. Therefore, both HFeCN and HFeNC could be candidates for their detection. We report geometrical parameters, vibrational frequencies, and rotational constants that could help with their experimental characterization.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13

Some Insights into Formamide Formation through Gas-phase Reactions in the Interstellar Medium

Producción CientíficaWe study the viability of different gas-phase ion–molecule reactions that could produce precursors of formamide in the interstellar medium. We analyze different reactions between cations containing a nitrogen atom (NH+3 , NH+4 , NH3OH+, and NH2OH+) and neutral molecules having one carbonyl group (H2CO and HCOOH). First, we report a theoretical estimation of the reaction enthalpies for the proposed processes. Second, for more favorable reactions, from a thermodynamic point of view, we perform a theoretical study of the potential energy surface. In particular, the more exothermic processes correspond to the reactions of ionized and protonated hydroxylamine with formaldehyde. In addition, a neutral–neutral reaction has also been considered. The analysis of the potential energy surfaces corresponding to these reactions shows that these processes present a net activation barrier and that they cannot be considered as a source of formamide in space.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13

Peptide bond formation through gas-phase reactions in the interstellar medium: Formamide and acetamide as prototypes

Producción CientíficaA theoretical study of the reactions of NH+4 with formaldehyde and CH+5 with formamide is carried out. The viability of these gas-phase ion–molecule reactions as possible sources of formamide and acetamide under the conditions of interstellar medium is evaluated. We report a theoretical estimation of the reaction enthalpies and an analysis of their potential energy surfaces. Formation of protonated formamide from the reaction between ammonium cation and formaldehyde is an exothermic process, but all the channels located on the potential energy surface leading to this product present net activation energies. For the reaction between methanium and formamide, different products are possible from a thermodynamic point of view. An analysis of its potential energy surface showed that formation of protonated acetamide and amino acetaldehyde takes place through barrier-free paths. Therefore, this reaction could be a feasible source of acetamide and amino acetaldehyde in spaceJunta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13

Generation and structural characterization of aluminum cyanoacetylide

Producción CientíficaCombined spectroscopy measurements and theoretical calculations bring to light a first investigation of a metallic cyanoacetylide, AlC3N, using laser ablation molecular beam Fourier transform microwave spectroscopy. This molecule was synthesized in a supersonic expansion by the reaction of aluminum vapour with C3N, produced from solid aluminum rods and BrCCCN in a newly constructed ablation-heating nozzle device. A set of accurate rotational and 27Al and 14N nuclear quadrupole coupling constants have been determined from the analysis of the rotational spectrum and compared with those predicted in a high-level ab initio study, conducting to the assignment of the observed species to linear AlCCCN. We have searched for this species towards the carbon-rich evolved star IRC + 10216 but only an upper limit to its abundance has been obtained.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13

Molecular Structure and Bonding in Plutonium Carbides: A Theoretical Study of PuC3

Producción CientíficaThe most relevant species of plutonium tricarbide were characterized using theoretical methods. The global minimum is predicted to be a fan structure where the plutonium atom is bonded to a quasi-linear C3 unit. A rhombic isomer, shown to be a bicyclic species with transannular C-C bonding, lies about 39 kJ/mol above the fan isomer. A linear PuCCC isomer and a three-membered ring CPuC2 isomer were found to be higher in energy (150 and 195 kJ/mol, respectively, above the predicted global minimum). The possible processes for the formation of these species are discussed, and the IR spectra were predicted to help in possible experimental detection. The nature of the Pu-C interaction has been analyzed in terms of a topological analysis of the electronic density, showing that Pu-C bonding is essentially ionic with a certain degree of covalent character.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13

Amino acetaldehyde conformers: structure and spectroscopic properties

Producción CientíficaWe present a computational study of the different conformers of amino acetaldehyde. This molecule is a precursor of glycine and also an isomer of the detected molecules acetaldehyde and methylformamide. In addition, a previous theoretical result shows that amino acetaldehyde could be formed from the gas phase reaction of formamide with CH+5⁠. Different computational approaches, going from density functional theory (DFT) to coupled cluster (CC) calculations, are employed for the characterization of the amino acetaldehyde conformers. We locate four low-lying conformation on the singlet potential energy surface (PES), two with a synperiplanar arrangement of the carboxylic oxygen atom and the NH2 group, and the other two conformers with an anticlinal disposition. All levels of theory predict the conformer with a synperiplanar arrangement and the H atoms of the NH2 group pointing in the direction of the oxygen, denoted as in-sp-amino acetaldehyde, as the most stable. The viability of the interconversion processes between the four conformers in space is analysed. Relevant spectroscopic parameters to rotational spectroscopy with ‘spectroscopic’ accuracy at the composite level are reported. Vibrational frequencies and infrared intensities are also computed at the CC with single and double excitations (CCSD) level including anharmonic corrections. This information could help in the experimental characterization of amino acetaldehyde that could be considered as a good candidate molecule to be searched for in space.Ministerio de Economía, Industria y Competitividad (Grant AYA2017-87515-P)Junta de Castilla y León (Ref. project VA010G18

Structure and spectroscopic properties of neutral and cationic tetratomic [C,H,N,Zn] isomers: A theoretical study

Producción CientíficaThe structure and spectroscopic parameters of the most relevant [C,H,N,Zn] isomers have been studied employing high-level quantum chemical methods. For each isomer, we provide predictions for their molecular structure, thermodynamic stabilities as well as vibrational and rotational spectroscopic parameters which could eventually help in their experimental detection. In addition, we have carried out a detailed study of the bonding situations by means of a topological analysis of the electron density in the framework of the Bader’s quantum theory of atoms in molecules. The analysis of the relative stabilities and spectroscopic parameters suggests two linear isomers of the neutral [C,H,N,Zn] composition, namely, cyanidehydridezinc HZnCN (1Σ) and hydrideisocyanidezinc HZnNC (1Σ), as possible candidates for experimental detections. For the cationic [C,H,N,Zn]+ composition, the most stable isomers are the ion-molecule complexes arising from the direct interaction of the zinc cation with either the nitrogen or carbon atom of either hydrogen cyanide or hydrogen isocyanide, namely, HCNZn+ (2Σ) and HCNZn+ (2Σ).Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13