Detection of interstellar PN: the first phosphorus-bearing species observed in molecular clouds

Prebiotic Astrochemistry from Astronomical Observations and Laboratory Spectroscopy

The discovery of more than 200 gas-phase chemical compounds in interstellar space has led to the speculation that this nonterrestrial synthesis may play a role in the origin of life. These identifications were possible because of laboratory spectroscopy, which provides the molecular fingerprints for astronomical observations. Interstellar chemistry produces a wide range of small, organic molecules in dense clouds, such as NH2COCH3, CH3OCH3, CH3COOCH3, and CH2(OH)CHO. Carbon (C) is also carried in the fullerenes C60 and C70, which can preserve C-C bonds from circumstellar environments for future synthesis. Elusive phosphorus has now been found in molecular clouds, the sites of star formation, in the molecules PO and PN. Such clouds can collapse into solar systems, although the chemical/physical processing of the emerging planetary disk is uncertain. The presence of molecule-rich interstellar starting material, as well as the link to planetary bodies such as meteorites and comets, suggests that astrochemical processes set a prebiotic foundation.

Structure and Spectroscopic Insights for CH3PCO Isomers: A High-Level Quantum Chemical Study

The exploration of phosphorus-bearing species stands as a prolific field in current astrochemical research, particularly within the context of prebiotic chemistry. Herein, we have employed high-level quantum chemistry methodologies to predict the structure and spectroscopic properties of isomers composed of a methyl group and three P, C, and O atoms. We have computed relative and dissociation energies, as well as rotational, rovibrational, and torsional parameters using the B2PLYPD3 functional and the explicitly correlated coupled cluster CCSD(T)-F12b method. Based upon our study, all the isomers exhibit a bent heavy atom skeleton with CH3PCO being the most stable structure, regardless of the level theory employed. Following in energy, we found four high-energy isomers, namely, CH3OCP, CH3CPO, CH3COP, and CH3OPC. The computed adiabatic dissociation energies support the stability of all [CH3, P, C, O] isomers against fragmentation into CH3 and [P, C, O]. Torsional barrier heights associated with the methyl internal rotation for each structure have been computed to evaluate the occurrence of possible A-E splittings in the rotational spectra. For the most stable isomer, CH3PCO, we found a V3 barrier of 82 cm-1, which is slightly larger than that obtained experimentally for the N-counterpart, CH3NCO, yet still very low. Therefore, the analysis of its rotational spectrum can be anticipated as a challenging task owing to the effect of the CH3 internal rotation. The complete set of spectroscopic constants and transition frequencies reported here for the most stable isomer, CH3PCO, is intended to facilitate eventual laboratory searches.

Prediction of vibrational spectrum and thermodynamic properties for phosphorus mononitride

In this work, an accurate potential energy curve (PEC) for the ground electronic state of phosphorus mononitride (PN) molecule has been determined from a variationally improved Hulburt-Hirschfelder (VIHH) oscillator model in conjunction with the experimental spectral constants (De,ωe,ωexe,Be,αe,re). We have numerically solved the Schrödinger equation for the VIHH potential using the LEVEL program, obtaining the pure vibrational spectrum that converges to the dissociation limit. In addition, the partition functions of PN molecule are calculated using the full rovibrational energies. Ultimately, thermodynamic properties like molar heat capacity, entropy, enthalpy, and Gibbs free energy were calculated for the PN molecule and show good agreement with those data from the NIST (National Institute of Standards and Technology) database.

A straightforward synthesis and physicochemical properties of chiral phosphorus-doped coronenes

Novel N,P-fused coronene derivatives have been successfully designed and achieved in one step using a three-fold Bischler-Napieralski cyclization as the key step. The unique structure, and tunable photophysical and electronic properties make them promising candidates for emissive and electron-transport materials.

Sources of Nitrogen-, Sulfur-, and Phosphorus-Containing Feedstocks for Prebiotic Chemistry in the Planetary Environment

Biochemistry on Earth makes use of the key elements carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (or CHONPS). Chemically accessible molecules containing these key elements would presumably have been necessary for prebiotic chemistry and the origins of life on Earth. For example, feedstock molecules including fixed nitrogen (e.g., ammonia, nitrite, nitrate), accessible forms of phosphorus (e.g., phosphate, phosphite, etc.), and sources of sulfur (e.g., sulfide, sulfite) may have been necessary for the origins of life, given the biochemistry seen in Earth life today. This review describes potential sources of nitrogen-, sulfur-, and phosphorus-containing molecules in the context of planetary environments. For the early Earth, such considerations may be able to aid in the understanding of our own origins. Additionally, as we learn more about potential environments on other planets (for example, with upcoming next-generation telescope observations or new missions to explore other bodies in our Solar System), evaluating potential sources for elements necessary for life (as we know it) can help constrain the potential habitability of these worlds.

Taming phosphorus mononitride

Phosphorus mononitride (PN) only has a fleeting existence on Earth, and molecular precursors for the release of this molecule under mild conditions in solution have remained elusive. Here we report the synthesis of an anthracene-based precursor-an anthracene moiety featuring an azidophosphine bridge across its central ring-that dissociates into dinitrogen, anthracene and P≡N in solution with a first-order half-life of roughly 30 min at room temperature. Heated under reduced pressure, this azidophosphine-anthracene precursor decomposes in an explosive fashion at around 42 °C, as demonstrated in a molecular-beam mass spectrometry study. The precursor is also shown to serve as a PN transfer reagent in the synthesis of an Fe-NP coordination complex, through ligand exchange with its Fe-N₂ counterpart. The terminal N-bonded complex was found to be energetically preferred, compared to its P-bonded linkage isomer, owing to a significant covalent Fe-pnictogen bond character and an associated less unfavourable Pauli repulsion in the metal-ligand interaction.

Ab Initio Study of Fine and Hyperfine Interactions in Triplet POH

Phosphorous-containing molecules have a great relevance in prebiotic chemistry in view of the fact that phosphorous is a fundamental constituent of biomolecules, such as RNA, DNA, and ATP. Its biogenic importance has led astrochemists to investigate the possibility that P-bearing species could have formed in the interstellar medium (ISM) and subsequently been delivered to early Earth by rocky bodies. However, only two P-bearing molecules have been detected so far in the ISM, with the chemistry of interstellar phosphorous remaining poorly understood. Here, in order to shed further light on P-carriers in space, we report a theoretical spectroscopic characterisation of the rotational spectrum of POH in its 3A″ ground electronic state. State-of-the-art coupled-cluster schemes have been employed to derive rotational constants, centrifugal distortion terms, and most of the fine and hyperfine interaction parameters, while the electron spin-spin dipolar coupling has been investigated using the multi-configuration self-consistent-field method. The computed spectroscopic parameters have been used to simulate the appearance of triplet POH rotational and ro-vibrational spectra in different conditions, from cold to warm environments, either in gas-phase experiments or in molecular clouds. Finally, we point out that the predicted hyperfine structures represent a key pattern for the recognition of POH in laboratory and interstellar spectra.

Frustrated Lewis Pair Stabilized Phosphoryl Nitride (NPO), a Monophosphorus Analogue of Nitrous Oxide (N2O)

Phosphoryl nitride (NPO) is a highly reactive intermediate, and its chemistry has only been explored under matrix isolation conditions so far. Here we report the synthesis of an anthracene (A) and phosphoryl azide based molecule (N₃P(O)A) that acts as a molecular synthon of NPO. Experimentally, N₃P(O)A dissociates thermally with a first-order kinetic half-life that is associated with an activation enthalpy of ΔH^⧧ = 27.5 ± 0.3 kcal mol^-1 and an activation entropy of ΔS^⧧ = 10.6 ± 0.3 cal mol^-1 K^-1 that are in good agreement with calculated DLPNO-CCSD(T)/cc-pVTZ//PBE0-D3(BJ)/cc-pVTZ energies. In solution N₃P(O)A undergoes Staudinger reactivity with tricyclohexylphosphine (PCy₃) and subsequent complexation with tris(pentafluorophenyl)borane (B(C₆F₅)₃, BCF) to form Cy₃P-NP(A)O-B(C₆F₅)₃. Anthracene is cleaved off photochemically to form the frustrated Lewis pair (FLP) stabilized NPO complex Cy₃P^⊕-N═P-O-B^⊖(C₆F₅)₃. An intrinsic bond orbital (IBO) analysis suggests that the adduct is zwitterionic, with a positive and negative charge localized on the complexing Cy₃P and BCF, respectively.

Diamidophosphate (DAP): A Plausible Prebiotic Phosphorylating Reagent with a Chem to BioChem Potential?

Known since the 1890s, diamidophosphate (DAP) has been investigated within the context of its inorganic chemistry. In 1999 - with the demonstration of DAP's potential as a phosphorylating agent of sugars in aqueous medium - began the exciting phase of research about DAP's role as a plausible prebiotic phosphorylating agent. More recently, in the last five years, there has been a steady increase in the publications that have documented the surprising versatility of DAP enabling the emergence of many classes of biomolecules of life, such as nucleic acids, peptides and protocells. Thus, though in its infancy, DAP seems to be uniquely positioned to play a central role in modelling abiotic- to prebiotic-chemical evolution. In this context, there is a need for systematic investigations for: (a) establishing DAP's likely availability on the early Earth, and (b) developing DAP's potential as a tool for use in synthetic and bioorganic chemistry.

Rovibronic spectroscopy of PN from first principles

We report an ab initio study on the rovibronic spectroscopy of the closed-shell diatomic molecule phosphorous mononitride, PN. The study considers the nine lowest electronic states, X 1Σ+, A 1Π, C 1Σ-, D 1Δ, E 1Σ-, a 3Σ+, b 3Π, d 3Δ and e 3Σ- using high level electronic structure theory and accurate nuclear motion calculations. The ab initio data cover 9 potential energy, 14 spin-orbit coupling, 7 electronic angular momentum coupling, 9 electric dipole moment and 8 transition dipole moment curves. The Duo nuclear motion program is used to solve the coupled nuclear motion Schrödinger equations for these nine electronic states and to simulate rovibronic absorption spectra of 31P14N for different temperatures, which are compared to available spectroscopic studies. Lifetimes for all states are calculated and compared to previous results from the literature. The calculated lifetime of the A1Π state shows good agreement with an experimental value from the literature, which is an important quality indicator for the ab initio A-X transition dipole moment.

In search of phosphorus in astronomical environments: The reaction between the CP radical (X2Σ+) and methanimine

Phosphorus is of particular interest in astrochemistry because it is a biogenic element together with hydrogen, carbon, nitrogen, oxygen, and sulfur. However, the chemical evolution of such element in the interstellar medium (ISM) is still far from an accurate characterization, with the chemistry of P-bearing molecules being poorly understood. To provide a contribution in this direction, we have carried out an accurate investigation of the potential energy surface for the reaction between the CP radical and methanimine (CH₂NH), two species already detected in the ISM. In analogy to similar systems, i.e., CH₂NH + X, with X = OH, CN, and CCH, this reaction can occur-from an energetic point of view-under the harsh conditions of the ISM. Furthermore, since the major products of the aforementioned reaction, namely, E- and Z-2-phosphanylidyneethan-1-imine (HN=CHCP) and N-(phosphaneylidynemethyl)methanimine (H₂C=NCP), have not been spectroscopically characterized yet, some effort has been made for filling this gap by means of accurate computational approaches.

Collisional excitation of interstellar PN by H2: New interaction potential and scattering calculations

Rotational excitation of interstellar PN molecules induced by collisions with H₂ is investigated. We present the first ab initio four-dimensional potential energy surface (PES) for the PN-H₂ van der Waals system. The PES was obtained using an explicitly correlated coupled cluster approach with single, double, and perturbative triple excitations [CCSD(T)-F12b]. The method of interpolating moving least squares was used to construct an analytical PES from these data. The equilibrium structure of the complex was found to be linear, with H₂ aligned at the N end of the PN molecule, at an intermolecular separation of 4.2 Å. The corresponding well-depth is 224.3 cm^-1. The dissociation energies were found to be 40.19 cm^-1 and 75.05 cm^-1 for complexes of PN with ortho-H₂ and para-H₂, respectively. Integral cross sections for rotational excitation in PN-H₂ collisions were calculated using the new PES and were found to be strongly dependent on the rotational level of the H₂ molecule. These new collisional data will be crucial to improve the estimation of PN abundance in the interstellar medium from observational spectra.

Insights into the reaction mechanism between phosphacyclopropenylidene and methyleneimine: A theoretical study

The reaction mechanism between phosphacyclopropenylidene and methyleneimine has been systematically investigated at the M06–2X/6–311++G(d,p) level of theory in order to better understand the reactivity of unsaturated cyclic phosphorus-bearing carbene. Geometry optimizations and vibrational analyses have been conducted for the stationary points on the potential energy surface of the system. Calculations show that the spiro bicyclic intermediate could be produced through the cycloaddition process between phosphacyclopropenylidene and methyleneimine initially. The reaction mechanism is illustrated with frontier molecular orbital theory. Introduction of electron-withdrawing group in phosphacyclopropenylidene will better facilitate the addition process. Through subsequent ring-expanding and hydrogen-migrating process, fuse-ring and allene compounds could be produced, respectively. Furthermore, it’s easy for spiro bicyclic intermediate and another methyleneimine to form a spiro tricyclic compound. This study is helpful to understand the reactivity of phosphacyclopropenylidene, the evolution of phosphorus-bearing molecules in space, and to offer an alternative approach to the formation of phosphorus-bearing heterocyclic compound.

Radiative lifetimes of vibrational levels and transition probabilities of spontaneous emissions of the six lowest-lying triplet states of AlN radical

The potential energy curves of 23 states of AlN radical are calculated to accurately determine the first several lowest-lying singlet and triplet states. The calculations are done using the CASSCF method, which is followed by the valence internally contracted MRCI approach. The rotationless radiative lifetimes of the vibrational levels are approximately 10^-7-10^-8 s for the C³Π, D³Π, and E³Δ states, 10¹-10^-4 s for the A³Σ^- state, and 10^-4-10^-5 s for the B³Σ⁺ state. The origins of the vibronic bands and the radiative lifetimes agree well with the available experimental and other theoretical results. The Einstein coefficients of many vibronic emissions are large for the C³Π-X³Π, C³Π-A³Σ^-, D³Π-X³Π, D³Π-A³Σ^-, and E³Δ-X³Π transitions and therefore, these transitions are strong. The emissions of the E³Δ-D³Π system are so weak that it is difficult to measure them through spectroscopy. The spectral distribution of the vibronic emissions is evaluated for the transitions of 12 pairs of states. In terms of the radiative lifetimes and transition probabilities obtained here, several spectroscopic routines for observing these states via spectroscopy are proposed.

Theoretical rotation-vibration spectroscopy of cis- and trans-diphosphene (P2H2) and the deuterated species P2HD

Growing astronomical interest in phosphorous (P) chemistry is stimulating the search for new interstellar P-bearing molecules, a task requiring detailed knowledge of the microwave and infrared molecular spectrum. In this work, we present comprehensive rotation-vibration line lists of the cis- and trans-isomers of diphosphene (P₂H₂). The line lists have been generated using robust, first-principles methodologies based on newly computed, high-level ab initio potential energy and dipole moment surfaces. Transitions are considered between states with energies up to 8000 cm^-1 and total angular momentum J ≤ 25. These are the first-ever line lists to be reported for P₂H₂, and they should significantly facilitate future spectroscopic characterization of this system. The deuterated species trans-P₂HD and the effect of its dynamic dipole moment on the rovibrational spectrum are also discussed.

Geochemical Sources and Availability of Amidophosphates on the Early Earth

Phosphorylation of (pre)biotically relevant molecules in aqueous medium has recently been demonstrated using water-soluble diamidophosphate (DAP). Questions arise relating to the prebiotic availability of DAP and other amidophosphosphorus species on the early earth. Herein, we demonstrate that DAP and other amino-derivatives of phosphates/phosphite are generated when Fe₃ P (proxy for mineral schreibersite), condensed phosphates, and reduced oxidation state phosphorus compounds, which could have been available on early earth, are exposed to aqueous ammonia solutions. DAP is shown to remain in aqueous solution under conditions where phosphate is precipitated out by divalent metals. These results show that nitrogenated analogues of phosphate and reduced phosphite species can be produced and remain in solution, overcoming the thermodynamic barrier for phosphorylation in water, increasing the possibility that abiotic phosphorylation reactions occurred in aqueous environments on early earth.

An interstellar synthesis of phosphorus oxoacids

Phosphorus signifies an essential element in molecular biology, yet given the limited solubility of phosphates on early Earth, alternative sources like meteoritic phosphides have been proposed to incorporate phosphorus into biomolecules under prebiotic terrestrial conditions. Here, we report on a previously overlooked source of prebiotic phosphorus from interstellar phosphine (PH3) that produces key phosphorus oxoacids-phosphoric acid (H3PO4), phosphonic acid (H3PO3), and pyrophosphoric acid (H4P2O7)-in interstellar analog ices exposed to ionizing radiation at temperatures as low as 5 K. Since the processed material of molecular clouds eventually enters circumstellar disks and is partially incorporated into planetesimals like proto Earth, an understanding of the facile synthesis of oxoacids is essential to untangle the origin of water-soluble prebiotic phosphorus compounds and how they might have been incorporated into organisms not only on Earth, but potentially in our universe as well.

Astrochemical evolution along star formation: Overview of the IRAM Large Program ASAI

Evidence is mounting that the small bodies of our Solar System, such as comets and asteroids, have at least partially inherited their chemical composition from the first phases of the Solar System formation. It then appears that the molecular complexity of these small bodies is most likely related to the earliest stages of star formation. It is therefore important to characterize and to understand how the chemical evolution changes with solar-type protostellar evolution. We present here the Large Program "Astrochemical Surveys At IRAM" (ASAI). Its goal is to carry out unbiased millimeter line surveys between 80 and 272 GHz of a sample of ten template sources, which fully cover the first stages of the formation process of solar-type stars, from prestellar cores to the late protostellar phase. In this article, we present an overview of the surveys and results obtained from the analysis of the 3 mm band observations. The number of detected main isotopic species barely varies with the evolutionary stage and is found to be very similar to that of massive star-forming regions. The molecular content in O- and C- bearing species allows us to define two chemical classes of envelopes, whose composition is dominated by either a) a rich content in O-rich complex organic molecules, associated with hot corino sources, or b) a rich content in hydrocarbons, typical of Warm Carbon Chain Chemistry sources. Overall, a high chemical richness is found to be present already in the initial phases of solar-type star formation.

Reactivity of phosphorus mononitride and interstellar formation of molecules containing phospazo linkage: A computational study on the reaction between HSi (X2Π) and PN (X1Σ+)

Phosphorus mononitride (PN) shows some interesting chemistry due to its low dissociation energy (compared to N2) and small dipole moment (zero dipole moment for N2). In this work, a reaction between HSi ([Formula: see text]) and PN ([Formula: see text]) has been studied using various computational methods. Analysis of the doublet surface of the [Formula: see text] reaction indicates that the reaction is exothermic in nature leading to the formation of various products. In view of the barrierless association of the reactants and exothermic nature for the product formation, it is suggested that species like HPNSi, cyclic-SiN(H)P (these two most stable isomers have phosphazo linkage) and HSiNP (third most stable isomer has phosphdiazo linkage) can possibly be detected in the interstellar medium. In view of the potential applications of phosphazo compounds in amide synthesis and pervasive nature of amide linkages in the nature, possible interstellar prebiotic applications can be advocated for these compounds.

Phosphorylation, oligomerization and self-assembly in water under potential prebiotic conditions

Prebiotic phosphorylation of (pre)biological substrates under aqueous conditions is a critical step in the origins of life. Previous investigations have had limited success and/or require unique environments that are incompatible with subsequent generation of the corresponding oligomers or higher-order structures. Here, we demonstrate that diamidophosphate (DAP)-a plausible prebiotic agent produced from trimetaphosphate-efficiently (amido)phosphorylates a wide variety of (pre)biological building blocks (nucleosides/tides, amino acids and lipid precursors) under aqueous (solution/paste) conditions, without the need for a condensing agent. Significantly, higher-order structures (oligonucleotides, peptides and liposomes) are formed under the same phosphorylation reaction conditions. This plausible prebiotic phosphorylation process under similar reaction conditions could enable the systems chemistry of the three classes of (pre)biologically relevant molecules and their oligomers, in a single-pot aqueous environment.

Nitrogenous Derivatives of Phosphorus and the Origins of Life: Plausible Prebiotic Phosphorylating Agents in Water

Phosphorylation under plausible prebiotic conditions continues to be one of the defining issues for the role of phosphorus in the origins of life processes. In this review, we cover the reactions of alternative forms of phosphate, specifically the nitrogenous versions of phosphate (and other forms of reduced phosphorus species) from a prebiotic, synthetic organic and biochemistry perspective. The ease with which such amidophosphates or phosphoramidate derivatives phosphorylate a wide variety of substrates suggests that alternative forms of phosphate could have played a role in overcoming the "phosphorylation in water problem". We submit that serious consideration should be given to the search for primordial sources of nitrogenous versions of phosphate and other versions of phosphorus.

HPCO-A Phosphorus-Containing Analogue of Isocyanic Acid

We describe the isolation and spectroscopic characterization of the heavier phosphorus-containing analogue of isocyanic acid (HPCO), and its isotopologue (DPCO). This fundamental small molecule, which has been postulated to exist in interstellar space, has thus far only been observed at low gas phase concentrations or in inert gas matrices. In this report we describe its synthesis, spectroscopic properties, and reactivity in solution.

Phosphinidene Reactivity of a Transient Vanadium P≡N Complex

Toward the preparation of a coordination complex of the heterodiatomic molecule PN, P≡N-V(N[^tBu]Ar)₃ (1, Ar = 3,5-Me₂C₆H₃), we report the use of ClPA (A = C₁₄H₁₀, anthracene) as a formal source of phosphorus(I) in its reaction with Na[NV(N[^tBu]Ar)₃] (Na[4]) to yield trimeric cyclo-triphosphane [PNV(N[^tBu]Ar)₃]₃ (3) with a core composed exclusively of phosphorus and nitrogen. In the presence of NapS₂ (peri-1,8-naphthalene disulfide), NapS₂P-NV(N[^tBu]Ar)₃ (6) is instead generated in 80% yield, suggesting trapping of transient 1. Upon mild heating, 3 readily fragments into dimeric [PNV(N[^tBu]Ar)₃]₂ (2), while in the presence of bis(trimethylsilyl)acetylene or cis-4-octene, the respective phosphirene (Ar[^tBu]N)₃VN-PC₂(SiMe₃)₂ (7) or phosphirane (Ar[^tBu]N)₃VN-P(C₈H₁₆) (8) compounds are generated. Kinetic data were found to be consistent with unimolecular decay of 3, and [2+1]-cycloaddition with radical clocks ruled out a triplet intermediate, consistent with intermediate 1 reacting as a singlet phosphinidene. In addition, both 7 and 8 were shown to reversibly exchange cis-4-octene and bis(trimethylsilyl)acetylene, serving as formal sources of 1, a reactivity manifold traditionally reserved for transition metals.

Prebiotic chemicals-amino acid and phosphorus-in the coma of comet 67P/Churyumov-Gerasimenko

The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples, a cometary origin was deduced from the (13)C isotopic signature. We report the presence of volatile glycine accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result demonstrates that comets could have played a crucial role in the emergence of life on Earth.

PROBING THE CARBON-PHOSPHORUS BOND COUPLING IN LOW-TEMPERATURE PHOSPHINE (PH3)-METHANE (CH4) INTERSTELLAR ICE ANALOGUES

Phosphine, which has now been confirmed around the carbon-rich star IRC+10216, provides the first example of a phosphorus-containing single bond in interstellar or circumstellar media. While four compounds containing both phosphorus and carbon have been discovered, none contain a carbon-phosphorus single bond. Here, we show that this moiety is plausible from the reaction of phosphine with methane in electron-irradiated interstellar ice analogues. Fractional sublimation allows for detection of individual products at distinct temperatures using reflectron time-of-flight mass spectrometry (ReTOF) coupled with vacuum ultraviolet photoionization. This method produced phosphanes and methylphosphanes as large as P8H10 and CH3P8H9, which demonstrates that a phosphorus-carbon bond can readily form and that methylphosphanes sublime at 12-17 K higher temperatures than the non-organic phosphanes. Also, irradiated ices of phosphine with deuterated-methane untangle the reaction pathways through which these methylphosphanes were formed and identified radical recombination to be preferred over carbene/phosphinidene insertion reactions. In addition, these ReTOF results confirm that CH3PH2 and CH6P2 can form via insertion of carbene and phosphinidene and that the methylenediphosphine (PH2CH2PH2) isomer forms in the ices, although methylphosphine (CH3P2H3) is likely the more abundant isomer and that phosphanes and organophosphanes preferentially fragment via the loss of a phosphino group when photoionized. While the formation of methylphosphine is overall endoergic, the intermediates produced by interactions with energetic electrons proceed toward methylphosphine favorably and barrierlessly and provide plausible mechanisms toward hitherto unidentified interstellar compounds.

Prebiotic chemical evolution in the astrophysical context

An ever increasing amount of molecular material is being discovered in the interstellar medium, associated with the birth and death of stars and planetary systems. Radio and millimeter-wave astronomical observations, made possible by high-resolution laboratory spectroscopy, uniquely trace the history of gas-phase molecules with biogenic elements. Using a combination of both disciplines, the full extent of the cycling of molecular matter, from circumstellar ejecta of dying stars - objects which expel large amounts of carbon - to nascent solar systems, has been investigated. Such stellar ejecta have been found to exhibit a rich and varied chemical content. Observations demonstrate that this molecular material is passed onto planetary nebulae, the final phase of stellar evolution. Here the star sheds almost its entire original mass, becoming an ultraviolet-emitting white dwarf. Molecules such as H2CO, HCN, HCO(+), and CCH are present in significant concentrations across the entire age span of such nebulae. These data suggest that gas-phase polyatomic, carbon-containing molecules survive the planetary nebula phase and subsequently are transported into the interstellar medium, seeding the chemistry of diffuse and then dense clouds. The extent of the chemical complexity in dense clouds is unknown, hindered by the high spectral line density. Organic species such as acetamide and methyl amine are present in such objects, and NH2CHO has a wide Galactic distribution. However, organophosphorus compounds have not yet been detected in dense clouds. Based on carbon and nitrogen isotope ratios, molecular material from the ISM appears to become incorporated into solar system planetesimals. It is therefore likely that interstellar synthesis influences prebiotic chemistry on planet surfaces.

Molecular properties of the PCO radical: heat of formation and the isomerization pathways

The potential energy surface of [P,C,O] system in the ground state was investigated by quantum chemical methods. Four different isomers were characterized at the B3LYP/aug-cc-pVTZ: COP (i1), cPCO (i2), PCO (i3), and CPO (i4). The linear species i3 is the global minimum in the ground state surface, while i4 is a bent structure, and i2 is a cyclic isomer. In view to evaluate the bond nature of each isomer, a QTAIM and a NBO analyses were applied. The triangular species presents a ring critical point which confirms its cyclic structure instead of a T-shape one. The stability increases in the following order: i3 > i2 > i1 > i4. The energy gap between i3 and i2 ranges from 49.20 to 51.15 kcal mol(-1). The reaction barrier energies that converge into the direction of i3 showed values around 10 kcal mol(-1), while the reverse barriers are considerably large (62.85 kcal mol(-1)). The i3 heat of formation at 298 K ranges from 11.83 to 19.41 kcal mol(-1).

Astrochemistry of transition metals? The selected cases of [FeN]+, [FeNH]+ and [(CO)2FeN]+: pathways toward CH3NH2 and HNCO

Transition metals are proposed to play an active role in the synthesis of organic compounds containing heteroatoms in astrochemistry.

The dynamics of the C + PH3 reaction: a theoretical study

The C + PH(3) reaction is one of the simplest gas-phase processes which can produce molecular species containing P-C bonds. It could be of astrophysical importance and a reference for other phosphine reactions with carbon-containing molecular radicals. The dynamical aspects have been studied theoretically by quasi-classical trajectory methods in order to determine its rate as a function of the temperature, the branching ratios, and the molecular mechanisms. We have obtained a T(0.2) dependence of the capture rate. The total rate is affected by the existence of relatively high-lying saddle points for the isomerization of the CPH(3) complex but get a value of 0.82·10(-10) cm(3) s(-1) at 300 K, which is considered quite high for a neutral-neutral reaction and higher than those of similar reactions. Moreover, the total rate presents a weak dependence with the temperature. Our results indicate that several products containing P-C bonds are formed, the main reaction channel being the generation of HPCH + H.