Electronic structure of simple phosphorus containing molecules [C,xH,O,P] candidate for astrobiology (x=1, 3, 5)

Characterizing the photodissociation dynamics of HPCO in the S1 band

A full-dimensional potential energy surface (PES) represented by the neural network method for the first excited state S1(1A″) of HPCO is reported for the first time. The PES was constructed based on more than 51 000 ab initio points, which were calculated at the multi-reference configuration interaction level with Davidson correction using the augmented correlation consistent polarized valence triple zeta basis set. Based on the newly constructed PES, quasi-classical trajectory calculations were carried out to study the photodissociation dynamics of HPCO at the total energy ranging from 4.0 to 5.6 eV. At low total energies, the HP + CO product is dominant, while the product H + PCO becomes increasingly favored at higher energies. Furthermore, the translational energy distributions of two products are found to be energy-dependent. Owing to the strongly repulsive PES along the HP + CO dissociation pathway, the translational energy distributions of HP + CO are dominated by relatively higher energies in contrast to H + PCO. The diatomic products HP and CO are found to possess the vibrational distributions decaying monotonically with the vibrational quantum number and relatively cold rotational state distributions, consistent with the strongly repulsive potentials toward the HP + CO channel. In addition, the vibrational distributions of HP and CO are found to be quite similar due to their close frequencies, while the rotational distributions of CO have a much more highly excited rotational degree of freedom owing to its rotational constant approximately four times smaller than that of HP.

Vibrational spectrum and photochemistry of phosphaketene HPCO

The vibrational spectra of the simplest phosphaketene HPCO and its isotopologue DPCO in solid Ar-matrices at 12.0 K have been analyzed with the aid of the computations at the CCSD(T)-F12a/cc-pVTZ-F12 level using configuration-selective vibrational configuration interaction (VCI). In addition to the four IR fundamentals, four overtone and ten combination bands have been unambiguously identified. Furthermore, the photochemistry of HPCO in the matrix has been investigated for the first time. Upon UV-light irradiation (365 or 266 nm), CO-elimination occurs by forming the parent phosphinidene HP that can be trapped by ˙NO to yield the elusive phosphinimine-N-oxyl radical HPNO˙. In contrast, an excimer laser (193 nm) irradiation of HPCO causes additional decomposition to H˙ and ˙PCO with concomitant formation of the long-sought phosphaethyne HOCP.

Oxidation of a phosphinidene oxide: formation of a dioxaphosphirane oxide with oxygen scrambling

The oxidation of a prototypical phosphinidene oxide FP[double bond, length as m-dash]O has been studied in O2-doped Ar and N2 matrices at 10 K. Upon 266 nm laser irradiation, FP[double bond, length as m-dash]O combines with O2 and yields the cyclic peroxide, dioxaphosphirane oxide FP([double bond, length as m-dash]O)(O2). Unexpected oxygen scrambling occurs during the oxygenation as evidenced by the observation of a 1 : 2 mixture of FP([double bond, length as m-dash]16O)(18O18O) and FP([double bond, length as m-dash]18O)(16O18O) when 18O2 was used. Quantum chemical calculations suggest that the scrambling happens via the intermediacy of the low-lying triplet FPO3 by passing minimum energy crossing points (MECPs). In addition, inorganic dioxophosphorane FP([double bond, length as m-dash]O)2 has been also identified among the oxidation products of FP[double bond, length as m-dash]O.

Quantum Chemical Calculations on CHOP Derivatives-Spanning the Chemical Space of Phosphinidenes, Phosphaketenes, Oxaphosphirenes, and COP- Isomers

After many decades of intense research in low-coordinate phosphorus chemistry, the advent of Na[OCP] brought new stimuli to the field of CHOP isomers and derivatives thereof. The present theoretical study at the CCSD(T)/def2-TZVPP level describes the chemical space of CHOP isomers in terms of structures and potential energy surfaces, using oxaphosphirene as the starting point, but also covering substituted derivatives and COP- isomers. Bonding properties of the P⁻C, P⁻O, and C⁻O bonds in all neutral and anionic isomeric species are discussed on the basis of theoretical calculations using various bond strengths descriptors such as WBI and MBO, but also the Lagrangian kinetic energy density per electron as well as relaxed force constants. Ring strain energies of the superstrained 1H-oxaphosphirene and its barely strained oxaphosphirane-3-ylidene isomer were comparatively evaluated with homodesmotic and hyperhomodesmotic reactions. Furthermore, first time calculation of the ring strain energy of an anionic ring is described for the case of oxaphosphirenide.

The Chemistry of the 2-Phosphaethynolate Anion

In all likelihood the first synthesis of the phosphaethynolate anion, PCO^- , was performed in 1894 when NaPH₂ was reacted with CO in an attempt to make Na(CP) accompanied by elimination of water. This reaction was repeated 117 years later when it was discovered that Na(OCP) and H₂ are the products of this remarkable transformation. Li(OCP) was synthesized and fully characterized in 1992 but this salt proved to be too unstable to allow for a detailed investigation of its chemistry. It was not until the heavier analogues of this lithium salt were isolated, Na(OCP) and K(OCP) (both of which are remarkably stable and can be even dissolved in water), that the chemistry of this new functional group could be explored. Here we review the chemistry of the 2-phosphaethynolate anion, a heavier phosphorus-containing analogue of the cyanate anion, and describe the wide breadth of chemical transformations for which it has been thus far employed. Its use as a ligand, in decarbonylative and deoxygenative processes, and as a building block for novel heterocycles is described. In the mere twenty-six years since Becker first reported the isolation of this remarkable anion, it has become a fascinating reagent for the synthesis of a vast library of, often unprecedented, molecules and compounds.

Methoxyphosphinidene and Isomeric Methylphosphinidene Oxide

A rare oxyphosphinidene (Me-OP) has been generated in the triplet ground state through either photolysis (266 nm) or flash-vacuum pyrolysis (FVP, 700 °C) of methoxydiazidophosphine MeOP(N₃)₂. Upon ArF laser irradiation (193 nm), an unprecedented isomerization from Me-OP to the long-sought methylphosphinidene oxide (Me-PO) occurs in cryogenic Ne- and N₂-matrices. Alternatively, the latter can be efficiently generated through photolysis (193 nm) or FVP (ca. 700 °C) of methylphosphoryl diazide MeP(O)(N₃)₂, in which the elusive nitrene intermediate MeP(O)(N₃)N in the triplet ground state has been also observed by IR (with ¹⁵N-labeling) and EPR (| D/ hc| = 1.545 cm^-1 and | E/ hc| = 0.003 95 cm^-1) spectroscopy.

Synthesis of the hitherto elusive formylphosphine (HCOPH2) in the interstellar medium - a molecule with an exotic phosphorus peptide bond

The formylphosphine (HCOPH2) molecule was detected in the gas phase via isomer selective photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS). Synthesized in carbon monoxide (CO)-phosphine ices (PH3) exposed to ionizing radiation, the formation mechanism involves an initial phosphorus-hydrogen bond rupture in phosphine yielding the phosphino radical (PH2) along with atomic hydrogen, addition of the suprathermal hydrogen atom to carbon monoxide leading to the formyl radical (HCO), and recombination of both radicals to formylphosphine (HCOPH2). This molecule represents the isovalent counterpart of the ubiquitous interstellar formamide (HCONH2). This study provides a fundamental framework to explore the synthesis and stability of the simplest isovalent counterpart of interstellar formamide (HCONH2) and suggests that formylphosphine (HCOPH2) should be detectable in the interstellar medium eventually providing a missing link between phosphorus-bearing complex organic molecules detected in the interstellar medium and on comet 67P/Churyumov-Gerasimenko.

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.

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).

Looking at radiation damage on prebiotic building blocks

A number of complex organic molecules have been detected in the interstellar medium, as well as in meteorites or comets. Among them, some exobiologic-relevant molecules have attracted particular interest. In the hypothesis of an exogen transport of prebiotic building blocks at the origin of life, the survival of such species and particularly their resistance to the solar UV radiation or cosmic rays is a key issue. For that purpose, we have performed a theoretical approach of the charge transfer dynamics induced by collision of protons with nucleobases and the 2-deoxy-d-ribose sugar moiety in a wide collision energy range. Calculations have been carried out by means of ab initio quantum chemistry molecular methods and compared to previous theoretical results using carbon projectile ions. Qualitative trends can be exhibited on DNA or RNA building blocks damage, which may concern studies on prebiotic species under spatial radiation.

Computational study of the reaction of P+ with acetylene: does spin-crossing play a significant role?

A computational study of the reaction of P(+)((3)P) with acetylene has been carried out. The only exothermic products correlating with the reactants are PCCH(+)((2)Π) + H((2)S). Two different pathways leading to these products that are apparently barrier-free have been found. Both pathways involve isomerization into open-chain intermediates followed by direct elimination of a hydrogen atom. The possibility of spin-crossing has been considered because the species on the singlet surface are considerably more stable than those on the triplet one. On the singlet surface, there are other possible channels for the reaction, namely, cyclic PC(2)H(+)((2)A') + H((2)S) and CCP(+)((1)Σ) + H(2) ((1)Σ(g)(+)). A computational kinetic study shows that, in agreement with the experimental evidence, the major products are PCCH(+)((2)Π) + H((2)S) at all temperatures. Only at very high temperatures is CCP(+)((1)Σ) + H(2) ((1)Σ(g)(+)) formed in non-negligible amounts. Therefore, only PCCH(+) should be formed in the interstellar medium.