Ionizing radiation exposure on Arrokoth shapes a sugar world.

The Kuiper Belt object (KBO) Arrokoth, the farthest object in the Solar System ever visited by a spacecraft, possesses a distinctive reddish surface and is characterized by pronounced spectroscopic features associated with methanol. However, the fundamental processes by which methanol ices are converted into reddish, complex organic molecules on Arrokoth's surface have remained elusive. Here, we combine laboratory simulation experiments with a spectroscopic characterization of methanol ices exposed to proxies of galactic cosmic rays (GCRs). Our findings reveal that the surface exposure of methanol ices at 40 K can replicate the color slopes of Arrokoth. Sugars and their derivatives (acids, alcohols) with up to six carbon atoms, including glucose and ribose-fundamental building block of RNA-were ubiquitously identified. In addition, polycyclic aromatic hydrocarbons (PAHs) with up to six ring units (13C22H12) were also observed. These sugars and their derivatives along with PAHs connected by unsaturated linkers represent key molecules rationalizing the reddish appearance of Arrokoth. The formation of abundant sugar-related molecules dubs Arrokoth as a sugar world and provides a plausible abiotic preparation route for a key class of biorelevant molecules on the surface of KBOs prior to their delivery to prebiotic Earth.

Reconsidering the Structures of C2 Al4 - and C2 Al5.

The study of C2 Al4 -/0 and C2 Al5 -/0 was conducted using anion photoelectron spectroscopy and quantum chemical computations. The present findings reveal that C2 Al4 - has a boat-like structure, with a single C2 unit surrounded by four aluminum atoms. In contrast, the neutral C2 Al4 species adopts a D2h planar structure with two planar tetracoordinate carbon (ptC) units, consistent with previous reports. Furthermore, the global minimum isomer of C2 Al5 - adopts a D3h symmetry, where the C2 unit interacts with five aluminum atoms. It was also found that a lower symmetry structure of C2 Al5 - , where all five aluminum atoms are located on the same side of the C2 unit, albeit slightly higher in energy compared to the D3h structure. These computations show that the D3h structure of C2 Al5 - is highly stable, exhibiting a large HOMO-LUMO gap.

Synthesis of interstellar propen-2-ol (CH3C(OH)CH2) - the simplest enol tautomer of a ketone.

Enols - tautomers of ketones or aldehydes - are anticipated to be ubiquitous in the interstellar medium and play a key role in the formation of complex organic molecules in deep space, but their fundamental formation mechanisms have remained largely elusive as of now. Here we present a combined experimental and computational study demonstrating the first preparation of propen-2-ol (CH3C(OH)CH2) and its isomer methyl vinyl ether (CH3OCHCH2) in low-temperature acetone (CH3COCH3) ices upon exposure to energetic electrons. Propen-2-ol is the simplest enol tautomer of a ketone. Exploiting tunable vacuum ultraviolet photoionization in conjunction with reflectron time-of-flight mass spectrometry, propen-2-ol and methyl vinyl ether were monitored in the gas phase upon sublimation during the temperature-programmed desorption process suggesting that both isomers are promising candidates for future astronomical searches such as via the James Webb Space Telescope. Electronic structure calculations reveal that the barrier of keto-enol tautomerization can be reduced by more than a factor of two (162 kJ mol-1) through the involvement of solvating water molecules under realistic conditions on interstellar grains. The implicit solvent effects, i.e., the influences of the solvent dipole field on the barrier height are found to be minimal and do not exceed 10 kJ mol-1. Our findings signify a crucial step toward a better understanding of the enolization of ketones in the interstellar medium thus constraining the molecular structures and complexity of molecules that form in extraterrestrial ices - ketones - through non-equilibrium chemistry.

Processing of methane and acetylene ices by galactic cosmic rays and implications to the color diversity of Kuiper Belt objects.

Kuiper Belt objects exhibit a wider color range than any other solar system population. The origin of this color diversity is unknown, but likely the result of the prolonged irradiation of organic materials by galactic cosmic rays (GCRs). Here, we combine ultrahigh-vacuum irradiation experiments with comprehensive spectroscopic analyses to examine the color evolution during GCR processing methane and acetylene under Kuiper Belt conditions. This study replicates the colors of a population of Kuiper Belt objects such as Makemake, Orcus, and Salacia. Aromatic structural units carrying up to three rings as in phenanthrene (C14H10), phenalene (C9H10), and acenaphthylene (C12H8), of which some carry structural motives of DNA and RNA connected via unsaturated linkers, were found to play a key role in producing the reddish colors. These studies demonstrate the level of molecular complexity synthesized of GCR processing hydrocarbon and hint at the role played by irradiated ice in the early production of biological precursor molecules.

Low-Temperature Thermal Formation of the Cyclic Methylphosphonic Acid Trimer [c-(CH3 PO2 )3 ].

We report the formation of the cyclic methylphosphonic acid trimer [c-(CH3 PO2 )3 ] through condensation reactions during thermal processing of low-temperature methylphosphonic acid samples exploiting photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) along with electronic structure calculations. Cyclic methylphosphonic acid trimers are formed in the solid state and detected together with its protonated species in the gas phase upon single photon ionization. Our studies provide an understanding of the preparation of phosphorus-bearing potentially prebiotic molecules and the fundamental knowledge of low-temperature phosphorus chemistry in extraterrestrial environments.

Structural Evolution of Carbon-Doped Aluminum Clusters AlnC- (n = 6-15): Anion Photoelectron Spectroscopy and Theoretical Calculations.

Carbon-doped aluminum cluster anions, AlnC- (n = 6-15), were generated by laser vaporization and investigated by mass-selected anion photoelectron spectroscopy. The geometric structures of AlnC- (n = 6-15) anions were determined by the comparison of theoretical calculations with the experimental results. It is found that the most stable structure of Al6C- is a carbon endohedral triangular prism. The Al7C- anion is a magic cluster with high stability. The structures of Al7-9C- can be viewed as the additional aluminum atoms attached around the triangular prism Al6C-. Two isomers of Al10C- have been detected in the experiments. The most stable one has a planar tetracoordinate carbon structure. The second one derives from Al9C- with the carbon atom located in a pentagonal bipyramid. The Al11C- anion has a bilayer structure composed of one planar tetracoordinate carbon and one aluminum-centered hexagon, in which the major interactions between two layers are multicenter bonds. The structures of Al12-14C- can be viewed as evolving from Al11C- by adding aluminum atoms to interact with the carbon atom. In Al15C-, the carbon atom stays at the surface with a tetracoordinate structure, and an icosahedral Al13 unit can be identified as a part of the geometric structure of Al15C-.

Formation of the elusive tetrahedral P3N molecule.

The tetrahedral 1,2,3-triphospha-4-azatricyclo [1.1.0.02,4] butane (P3N) molecule-an isovalent species of phosphorus (P4)-was prepared in low-temperature (5 K) phosphine-nitrogen ices and was identified in the gas phase through isomer-selective, tunable, soft photoionization reflectron time-of-flight mass spectrometry. Theoretical calculations reveal that the substitution of a single phosphorus atom by nitrogen in the P4 molecule results in enhanced spherical aromaticity while simultaneously increasing the strain energy from 74 to 195 kJ mol-1. In P3N, the P─P bond is shortened compared to those in P4 by 3.6 pm, while the P─N─P bond angle of 73.0° is larger by 13.0° compared to the P─P─P bond angle of 60.0° in P4. The identification of tetrahedral P3N enhances our fundamental understanding of the chemical bonding, electronic structure, and stability of binary, interpnictide tetrahedral molecules and reveals a universal route to prepare ring strained cage molecules in extreme environments.

Detection of 1H-Triphosphirene (c-HP3) and 2-Triphosphenylidene (HP3): The Isovalent Counterparts of 1H-Triazirine (c-HN3) and Hydrazoic Acid (HN3).

The hitherto elusive 1H-triphosphirene (c-HP3) and 2-triphosphenylidene (HP3) molecules were prepared in low-temperature matrices and detected isomer selectively through photoionization coupled with reflectron time-of-flight mass spectrometry (PI-ReTOF-MS). Our results reveal a thermodynamically preferred cyclic isomer (c-HP3) compared to the acyclic structure (HP3) in contrast to the isovalent HN3 system favoring hydrazoic acid (HN3) compared to 1H-triazirine (c-HN3). Theoretical computations suggest a ring strain energy of 1H-triphosphirene (c-HP3) of only 35 kJ mol-1, which is significantly lower than the tetrahedral phosphorus molecule (P4) of 74 kJ mol-1. This work provides a fundamental benchmark to understand the electronic structure and chemical bonding of cyclic molecules and offers an unconventional approach to preparing highly strained, still elusive molecules such as 1H-triazirine and tetrahedral tetranitrogen (N4) in the near future involving progressive nonequilibrium chemistries.

Photoelectron spectroscopy and theoretical study of AlnC5-/0 (n = 1-5) clusters: structural evolution, relative stability of star-like clusters, and planar tetracoordinate carbon structures.

The AlnC5- (n = 1-5) clusters were detected in the gas-phase and were investigated via mass-selected anion photoelectron spectroscopy. The structures of AlnC5-/0 (n = 1-5) were explored by theoretical calculations. It is found that the structures of AlC5-/0 and Al2C5-/0 are linear while those of Al3C5-/0, Al4C5-/0, and Al5C5-/0 are two-dimensional. The most stable structures of AlC5-/0 and Al2C5-/0 are linear with the Al atoms attached to the ends of C5 chain. The most stable structures of Al3C5-/0 can be viewed as three Al atoms interacting with a nonlinear C5 chain. The most stable structure of Al4C5- anion is a planar structure composed of a C2 unit, a C3 unit, and two Al2 units, while that of the neutral Al4C5 cluster has four Al atoms connected to different positions of a distorted C5 chain. The global minimum structures of Al5C5-/0 are planar structures composed of an Al4C quadrilateral, two C2 groups, and an Al atom connected to two C2 groups. Planar tetracoordinate carbon (ptC) has been identified in the structures of both anionic and neutral Al5C5. It is worth mentioning that the star-like structure of Al5C5- is slightly higher in energy than the ground state structure. The comparison of theoretical calculations with the experimental spectra indicates the star-like structure of Al5C5- may also appear in our experiments.

Anion Photoelectron Spectroscopy and Theoretical Studies of Al4C6-/0: Global Minimum Triangle-Shaped Structures and Hexacoordinated Aluminum.

Anion photoelectron spectroscopy and theoretical calculations were used to investigate the structural and bonding properties of Al4C6-/0 clusters. The vertical detachment energy of Al4C6- was measured to be 3.36 ± 0.08 eV. The structure of the Al4C6- anion is confirmed to be a bowl-shaped distorted triangle with an Al atom at the center and three Al atoms at the vertices. The global minimum isomer of neutral Al4C6 has a planar triangle-shaped structure with D3h symmetry. Both anionic and neutral Al4C6 have a hexacoordinated Al atom surrounded by three C≡C groups. Compared with the structure of neutral Al4C6, the structure of Al4C6- is distorted due to the addition of the excess electron. The molecular orbital analysis shows that the singly occupied molecular orbital of Al4C6- mainly locates on one side of the triangle plane and the neutral Al4C6 has a large highest occupied molecular orbital and lowest unoccupied molecular orbital gap. Theoretical calculations indicate that neutral Al4C6 has some aromaticity.

Size-selected anion photoelectron spectroscopy and density functional theory study of MnCn -/0 (n = 3-10): Odd-even alternation and linear-cyclic structure competition.

The structural and electronic properties of MnCn - (n = 3-10) clusters have been investigated using size-selected photoelectron spectroscopy and density functional theory calculations. The vertical detachment energies of MnCn - exhibit a strong odd-even alternation with increasing number of carbon atoms: the vertical detachment energies of MnCn - containing even number of carbon atoms are higher than those of adjacent ones containing odd number of carbon atoms. The theoretical analyses indicate that the spin multiplicities and relative stabilities of MnCn -/0 also exhibit odd-even alternations. It is found that MnC3 - has three degenerate isomers with two linear structures in different electronic states and one fanlike structure. For n = 4-6, 8, and 10, the ground state structures are all linear with the Mn atom at one end. MnC7 - and MnC9 - have cyclic structures. As for the neutral species, MnC3 and MnC4 adopt fan-shaped structures, MnC5 has a linear structure, and MnC6-10 have cyclic configurations. The atomic dipole moment corrected Hirshfeld population analysis shows that the electrons transfer from the Mn atom to the Cn units. The total spin magnetic moments of MnCn -/0 (n = 3-10) clusters are mainly contributed by the local magnetic moments on the Mn atom.