On the Formation of the Popcorn Flavorant 2,3-Butanedione (CH3COCOCH3) in Acetaldehyde-Containing Interstellar Ices

Acetaldehyde (CH₃CHO) is ubiquitous throughout the interstellar medium and has been observed in cold molecular clouds, star forming regions, and in meteorites such as Murchison. As the simplest methyl-bearing aldehyde, acetaldehyde constitutes a critical precursor to prebiotic molecules such as the sugar deoxyribose and amino acids via the Strecker synthesis. In this study, we reveal the first laboratory detection of 2,3-butanedione (diacetyl, CH₃COCOCH₃) – a butter and popcorn flavorant – synthesized within acetaldehyde-based interstellar analog ices exposed to ionizing radiation at 5 K. Detailed isotopic substitution experiments combined with tunable vacuum ultraviolet (VUV) photoionization of the subliming molecules demonstrate that 2,3-butanedione is formed predominantly via the barrier-less radical–radical reaction of two acetyl radicals (CH₃ĊO). These processes are of fundamental importance for a detailed understanding of how complex organic molecules (COMs) are synthesized in deep space thus constraining the molecular structures and complexity of molecules forming in extraterrestrial ices containing acetaldehyde through a vigorous galactic cosmic ray driven non-equilibrium chemistry.     

Interstellar matrices: the chemical composition and evolution of interstellar ices as observed by ISO

Matrix isolation techniques have been developed in the early sixties as a tool for studying the spectroscopic properties of out of equilibrium species (atoms, radicals, ions, reactive molecules), embedded in rare gas inert matrices at low temperatures. Cold interstellar grains surfaces are able to condense out gas phase molecules, routinely observed by radioastronomy. These grain 'mantles' can be considered as 'interstellar matrices'. However, these matrices are not clean and unreactive. They are made principally of dirty ices whose composition must be determined carefully to assess the importance of the solid state chemistry that takes place in the Interstellar Medium. Infrared spectroscopy, both in astronomy and in the laboratory, is the unique tool to determine the chemical composition of these ices. Astronomical spectra can directly be compared with laboratory ones obtained using classical matrix isolation techniques. Furthermore, dedicated experiments may be undertaken to further improve the understanding of the basic physico-chemical processes that take place in cosmic ices.     

Efficient surface formation route of interstellar hydroxylamine through NO hydrogenation. I. The submonolayer regime on interstellar relevant substrates

Dust grains in the interstellar medium are known to serve as the first chemical laboratory where the rich inventory of interstellar molecules are synthesized. Here we present a study of the formation of hydroxylamine-NH(2)OH-via the non-energetic route NO + H (D) on crystalline H(2)O and amorphous silicate under conditions relevant to interstellar dense clouds. Formation of nitrous oxide (N(2)O) and water (H(2)O, D(2)O) is also observed and the reaction network is discussed. Hydroxylamine and water results are detected in temperature-programmed desorption (TPD) experiments, while N(2)O is detected by both reflection-absorption IR spectroscopy and TPD techniques. The solid state NO + H reaction channel proves to be a very efficient pathway to NH(2)OH formation in space and may be a potential starting point for prebiotic species in dark interstellar clouds. The present findings are an important step forward in understanding the inclusion of interstellar nitrogen into a non-volatile aminated species since NH(2)OH provides a solid state nitrogen reservoir along the whole evolutionary process of interstellar ices from dark clouds to planetary systems.     

On the formation of ozone in oxygen-rich solar system ices via ionizing radiation

The irradiation of pure molecular oxygen (O(2)) and carbon dioxide (CO(2)) ices with 5 keV H(+) and He(+) ions was investigated experimentally to simulate the chemical processing of oxygen rich planetary and interstellar surfaces by exposure to galactic cosmic ray (GCR), solar wind, and magnetospheric particles. Deposited at 12 K under ultra-high vacuum conditions (UHV), the irradiated condensates were monitored on-line and in situ in the solid-state by Fourier transform infrared spectroscopy (FTIR), revealing the formation of ozone (O(3)) in irradiated oxygen ice; and ozone, carbon monoxide (CO), and cyclic carbon trioxide (c-CO(3)) in irradiated carbon dioxide. In addition to these irradiation products, evolution of gas-phase molecular hydrogen (H(2)), atomic helium (He) and molecular oxygen (O(2)) were identified in the subliming oxygen and carbon dioxide condensates by quadrupole mass spectrometry (QMS). Temporal abundances of the oxygen and carbon dioxide precursors and the observed molecular products were compiled over the irradiation period to develop reaction schemes unfolding in the ices. These reactions were observed to be dependent on the generation of atomic oxygen (O) by the homolytic dissociation of molecular oxygen induced by electronic, S(e), and nuclear, S(n), interaction with the impinging ions. In addition, the destruction of the ozone and carbon trioxide products back to the molecular oxygen and carbon dioxide precursors was promoted over an extended period of ion bombardment. Finally, destruction and formation yields were calculated and compared between irradiation sources (including 5 keV electrons) which showed a surprising correlation between the molecular yields (～10(-3)-10(-4) molecules eV(-1)) created by H(+) and He(+) impacts. However, energy transfer by isoenergetic, fast electrons typically generated ten times more product molecules per electron volt (～10(-2)-10(-3) molecules eV(-1)) than exposure to the ions. Implications of these findings to Solar System chemistry are also discussed.     

Do Xylylenes Isomerize in Pyrolysis?

We report infrared spectra of xylylene isomers in the gas phase, using free electron laser (FEL) radiation. All xylylenes were generated by flash pyrolysis. The IR spectra were obtained by monitoring the ion dip signal, using a IR/UV double resonance scheme. A gas phase IR spectrum of para-xylylene  was recorded, whereas ortho- and meta-xylylene were found to partially rearrange to benzocyclobutene and styrene. Computations of the UV oscillator strength  for all molecules were carried out and provde an explanation for the observation of the isomerization products.     

Crystal structures and thermal decomposition mechanism of four lanthanide complexes with halogen-benzoic acid and 1,10-phenanthroline

This paper describes syntheses and structure determination of four lanthanide complexes [Nd(2-Cl-4-FBA) 3 phen] 2 (1, 2-Cl-4-FBA = 2-chloro-4-fluorobenzoate, phen = 1,10-phenanthroline), [Ln(2,5-DClBA) 3 phen] 2 (Ln = Sm(2) and Tb(3), 2,5-DClBA = 2,5-dichlorobenzoate) and [Sm(2-Cl-4,5-DFBA) 3 (phen)(H 2 O)] 2 (4, (2-Cl-4,5-DFBA = 2-chloro-4,5-difluorobenzo- ate). The complexes were characterized by elemental analysis, infrared and ultraviolet spectra, and X-ray single-crystal diffraction. In the molecular structures of 1 4, two Ln 3+ ions are linked by four carboxyl groups, with two of them in a bridging bidentate mode and the other two in a bridging-chelating tridentate mode, forming four binuclear molecules. In addition, each Ln 3+ ion is also chelated to one phen molecule and one carboxyl group in the complexes, except each Sm 3+ ion in 4 which is bonded to one carboxyl group by unidentate mode and one H 2 O molecule. There are two different coordination polyhedrons for each Nd 3+ ion in the two similar molecular structures of 1 and they are a distorted monocapped square antiprismatic and a distorted tricapped triangular prism conformation, respectively. The coordination polyhedron for each Ln 3+ ion in 2 4 is a nine-coordinated distorted mono-capped square antiprismatic conformation. The complex 3 exhibits green luminescence under the radiation of UV light. The thermal decomposition behaviors of the complexes have been discussed by simultaneous TG/DSC-FTIR technique. The 3D surface graphs for the FTIR spectra of the evolved gases were recorded and the gaseous products were identified by the typical IR spectra obtained at different temperatures from the 3D surface graphs. Meanwhile, we discussed the nonisothermal kinetics of 1 4 by the integral isoconversional non-linear (NL-INT) method.     

New class of organic-inorganic hybrid aggregates based on polyoxometalates and metal-Schiff-base

By combination of heteropolymolybdates and metal-Schiff-base complexes, two new organic-inorganic hybrid compounds {Mn(salen)(2)(H(2)O)(2)[AlMo(6)(OH)(6)O(18)]}[arg]·16H(2)O (1) and {Mn(salen)(2)(H(2)O)(2)[CrMo(6)(OH)(6)O(18)]}[arg]·11H(2)O (2) (salen = N,N'-ethylene-bis(salicylideneiminate) have been successfully isolated. Compounds 1 and 2 were structurally characterized by elemental analyses, IR spectra, thermogravimetric analysis, and single-crystal X-ray diffraction. To the best of our knowledge, compounds 1 and 2 represent the first single-crystal structures of metal-Schiff-base decorated polyoxometalates (POMs) compounds. Photocatalytic experiments indicated that both 1 and 2 exhibit high catalytic activity for photodegradation of RhB with UV irradiation. In addition, the magnetic properties of 1 were also investigated.     

粉状白钨酸的研究——ⅩⅤ.利用粉状白钨酸的离子交换性能直接制备一价阳离子的十聚钨酸盐

以粉状白钨酸为原料,利用它的离子交换性能制得了碱金属及铵的酸式十聚钨酸盐M_3HW_(10)O_(32)·11H_20(M=NH_4、Li、Na、K)。测定了它们的差热分析、X-射线粉末衍射、IR和UV光谱,在水溶液中的稳定性以及光致变色等性质。     

IR STUDIES ON MECHANISM OF DIRECT OXIDATION OF METHANE TO SYNTHESIS GAS OVER A Ni/Al2O3 CATALYS

The mechanism of the CH4/O2 to syngas reaction has been investigated by FT-IR over a 2.9%(wt)Ni/Al2O3. IR spectra of adsorption of CH4 indicate that chemisorbed O atoms can react selectively with active carbon species (arising from CH4 decomposition) to give CO. IR spectra of adsorption of CH4/O2(2:1 mole ratio) mixture show that CO2 and H2O are the detectable products with no CO, revealing that the reforming of remaining CH4 would not take place. We propose that CO and H2 are primary products in this reaction.     

硼合多羟基醇希土配合物的合成与性质及其配位作用的研究

本文合成了硼合甘油希土和硼合葡萄糖希土二类共八个配合物。用化学分析、红外光谱、紫外光谱及热谱确定其组成为:RE(BO_2·C_3H_8O_3)_3·nCH_3OH和RE(BO_2·C_6H_(12)O_6)_3·3H_2O(RE=Nd、Gd、Y、Yb)。摩尔电导测定表明这两类化合物均为中性配合物。红外光谱显示出硼与多羟基醇之间以硼氧四面体形式结合。本文还通过电位滴定法讨论了希土与硼合多羟基醇之间的配位作用。     

Infrared action spectra of Ca2+(H2O)(11-69) exhibit spectral signatures for condensed-phase structures with increasing cluster size

Infrared laser action spectroscopy is used to characterize divalent calcium ions solvated by up to 69 water molecules. The spectrum for Ca(2+)(H2O)12 indicates that in the predominant structure, eight inner-shell water molecules solvate the metal ion and donate one hydrogen bond to one of four second-shell, double-acceptor water molecules. Eight-coordinate solvation is consistent with results from many condensed-phase studies, and contrasts with results for smaller gas-phase clusters that are most consistent with six-coordinate solvation. Each water molecule in this structure of Ca(2+)(H2O)12 coordinates with two other members of the cluster. With increasing cluster size, the number of two-coordinate water molecules decreases, whereas that of three-coordinate water molecules increases. The number of one-coordinate water molecules increases until n approximately 18, but they are essentially depleted by n approximately = 30. Spectra of the largest clusters, which have effective concentrations of divalent calcium that are less than 1 M, exhibit only subtle changes with increasing cluster size. The bonded-OH regions of these spectra are similar to, but blue-shifted from that of bulk water, whereas the free-OH regions are well-resolved and indicate that the surfaces of these clusters are well-structured. These results comprise the most extensive vibrational spectroscopic study yet performed on metal ion hydration in the gas phase and provide insights into metal ion solvation in bulk and interfacial environments.     

An experimental and theoretical study on the interaction of PHBA ions and H2O molecules

We studied the dependence of the Raman spectra on the concentration of PHBA aqueous solution under UV laser excitation. Through analyzing the spectra, we conclude that the interaction between PHBA ions and H(2)O molecules is weak. To further explore the problem, we studied the interaction between PHBA ions and H(2)O molecules by virtue of theoretical calculations, DFT-B3PW91/6-31+g(*) was employed. We draw a coincident conclusion with the experiments and dug out the reasonable interaction model that reflects the actual interaction configuration between PHBA ions and H(2)O molecules. We supply a new thinking for studying interactions between solute molecules and solvent molecules, which also can be applied to interactions between solute molecules and other solute molecules in solutions.     

Cyanides,Isocyanides, and Hydrides of Zn,Cd and Hg from Metal Atom and HCN Reactions: Matrix Infrared Spectra and Electronic Structure Calculations

Zinc and cadmium atoms from laser ablation of the metals and mercury atoms ablated from a dental amalgam target react with HCN in excess argon during deposition at 5 K to form the MCN and MNC molecules and CN radicals. UV irradiation decreases the higher energy ZnNC isomer in favor of the lower energy ZnCN product. Cadmium and mercury atoms produce analogous MCN primary molecules. Laser ablation of metals also produces plume radiation which initiates H-atom detachment from HCN. The freed H atom can add to CN radical to produce the HNC isomer. The argon matrix also traps the higher energy but more intensely absorbing isocyanide molecules. Further reactions with H atoms generate HMCN and HMNC hydrides, which can be observed by virtue of their C−N stretches and intense M−H stretches. Computational modeling of IR spectra and relative energies guides the identification of reaction products by providing generally reliable frequency differences within the Zn, Cd and Hg family of products, and estimating isotopic shifts using to ¹³C and ¹⁵N isotopic substitution for comparison with experimental data.     

Cd-Ln杂双核配合物的合成、结构及发光性质

采用混合溶剂热方法合成了3个新颖的杂双核d-f配合物, [LnCd(C8H7O3)5(phen)(H2O)](Ln=Dy(1), Pr(2), Gd(3); C8H7O3=对甲氧基苯甲酸根, phen=1,10-菲啰啉), 通过单晶X射线衍射确定了配合物的晶体结构. 结果表明, 3个化合物是同构的. 在同一个分子中, Cd2+与Ln3+通过3个对甲氧基苯甲酸根桥联, Cd2+为五配位, Ln3+为八配位. 在晶体中, 两个相邻的分子被氢键连成二聚体. 测定了3个配合物在室温下的IR, UV-Vis-NIR以及激发和发射光谱. 对比分析了化合物的UV-Vis-NIR吸收光谱与发射光谱的关系, 讨论了d-块(d-L部分)对Ln3+发光的影响.     

Synthesis of [MnCl<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>(Hatz)]·H<Subscript>2</Subscript>O and investigation of its structure via X-ray diffraction,spectroscopic measurements and DFT calculations

The 3-amino-1,2,4-triazole (atz)-based manganese complex was prepared and characterized through single-crystal X-ray diffraction, IR, EPR, and UV–visible spectroscopy. In the crystal structure, individual complex are interconnected through N(O)–H…Cl hydrogen bonds into 1D undulating chains running parallel to the [110] direction of the unit cell. Chains further grow into 2D supramolecular layers by way of the lattice water molecules of coordination and the chloride anions (O–H…Cl). Layers pack along the b-axis of the unit cell mediated by O–H…Cl(N) and N–H…O(Cl) hydrogen bonds forming a 3D supramolecular architecture. The theoretical calculations were also performed to optimize the structure of the complexes in the gas phase to confirm the structures proposed by X-ray crystallography. In addition, IR and UV–visible spectra of complex were calculated and compared with the corresponding experimental spectra to complete the experimental structural identification. The three-dimensional Hirshfeld surface (3D-HS) and their relative two-dimensional fingerprint plots (2D-FP) reveal that the structure is dominated by H…Cl/Cl…H (50.5%), H…O/O…H (11.3%) and N…O/O…N (10.2%) contacts.     

Secondary ion emission induced by fission fragment impact in CO-NH(3) and CO-NH(3)-H(2)O ices: modification in the CO-NH(3) ice structure

CO-NH(3) and CO-NH(3)-H(2)O ices at 25-130 K were bombarded by (252)Cf fission fragments ( approximately 65 MeV at the target surface) and the emitted secondary ions were analyzed by time-of-flight mass spectrometry (TOF-SIMS). It is observed that the mass spectra obtained from both ices have similar patterns. The production of hybrid ions (formed from CO and NH(3) molecules) emitted from CO-NH(3) ice has already been reported by R. Martinez et al., Int. J. Mass. Spectrom. 262 (2006) 195; here, the secondary ion emission and the modifications of the CO--NH(3) ice structure during the temperature increase of the ice are addressed. These studies are expected to throw light on the sputtering from planetary and interstellar ices and the possible formation of new organic molecules in CO-NH(3)-H(2)O ice by megaelectronvolt ion bombardment. The presence of water in the CO-NH(3) ice mixture generates molecular ion series such as (NH(3))(p-q)(H(2)O)(q)CO(+) and replaces the cluster series (NH(3))(n)NH(4) (+) emission by the hybrid series (NH(3))(I-i)(H(2)O)(i=1, 2...I)H(+). The distribution of NH(3) and H(2)O molecules within the cluster groups indicates that ammonia and water mix homogeneously in the icy condensate at T = 25 K. The desorption yield distribution of the cluster series (NH(3))(n)NH(4) (+) is described by the sum of two exponential functions: one, slow-decreasing, attributed to the fragmentation of the solid target into clusters; and another, fast-decreasing, due to a local sublimation followed by recombination of ammonia molecules. The analysis of the time-temperature dependence of these two yield components gives information on the formation process of molecular ions, the transient composition of the ice target and structural changes of the ice. Data suggest that the amorphous and porous structure of the NH(3) ice, formed by the condensation of the CO--NH(3) gas at T = 25 K, survives CO sublimation until the occurrence of a phase transition around 80 K, which produces a more fragile ice structure.     

Zinc and cadmium dihydroxide molecules: matrix infrared spectra and theoretical calculations

Laser-ablated zinc and cadmium atoms were mixed uniformly with H2 and O2 in excess argon or neon and with O2 in pure hydrogen or deuterium during deposition at 8 or 4 K. UV irradiation excites metal atoms to insert into O2 producing OMO molecules (M = Zn, Cd), which react further with H2 to give the metal hydroxides M(OH)2 and HMOH. The M(OH)2 molecules were identified through O-H and M-O stretching modes with appropriate HD, D2, (16,18)O2, and (18)O2 isotopic shifts. The HMOH molecules were characterized by O-H, M-H, and M-O stretching modes and an M-O-H bending mode, which were particularly strong in pure H2/D2. Analogous Zn and Cd atom reactions with H2O2 in excess argon produced the same M(OH)2 absorptions. Density functional theory and MP2 calculations reproduce the IR spectra of these molecules. The bonding of Group 12 metal dihydroxides and comparison to Group 2 dihydroxides are discussed. Although the Group 12 dihydroxide O-H stretching frequencies are lower, calculated charges show that the Group 2 dihydroxide molecules are more ionic.     

Reactions of late lanthanide metal atoms with water molecules: a matrix isolation infrared spectroscopic and theoretical study

The reactions of late lanthanide metal atoms (Gd-Lu) with water molecules have been investigated using matrix isolation infrared spectroscopy. The reaction intermediates and products were identified on the basis of isotopic substitution experiments and density functional theory calculations. All of the metal atoms except Lu react with water to form the M(H2O) complexes spontaneously upon annealing (M = Gd, Tb, Dy, Ho, Er, Tm, and Yb). The Dy(H2O) and Ho(H2O) complexes are able to coordinate a second water molecule to form the Dy(H2O)2 and Ho(H2O)2 complexes. The M(H2O) complexes isomerize to the inserted HMOH isomers under visible light irradiation, which further decompose to give the MO and/or HMO molecules upon UV light irradiation. The M(OH)2 molecules (M = Gd-Lu) were also produced. The results have been compared with our earlier work covering the early lanthanide metal atoms (Nd, Sm, Eu) to observe the existent trends for the lanthanide metal atom reactions.     

Photochemistry of hydrogen halides on water clusters: simulations of electronic spectra and photodynamics, and comparison with photodissociation experiments

The photochemistry of small HX·(H(2)O)(n), n = 4 and 5 and X = F, Cl, and Br, clusters has been modeled by means of ab initio-based molecular simulations. The theoretical results were utilized to support our interpretation of photodissociation experiments with hydrogen halides on ice nanoparticles HX·(H(2)O)(n), n ≈ 10(2)-10(3). We have investigated the HX·(H(2)O)(n) photochemistry for three structural types: covalently bound structures (CBS) and acidically dissociated structures in a form of contact ion pair (CIP) and solvent separated pair (SSP). For all structures, we have modeled the electronic absorption spectra using the reflection principle combined with a path integral molecular dynamics (PIMD) estimate of the ground state density. In addition, we have investigated the solvent effect of water on the absorption spectra within the nonequilibrium polarizable continuum model (PCM) scheme. The major conclusion from these calculations is that the spectra for ionic structures CIP and SSP are significantly red-shifted with respect to the spectra of CBS structures. We have also studied the photodynamics of HX·(H(2)O)(n) clusters using the Full Multiple Spawning method. In the CBS structures, the excitation led to almost immediate release of the hydrogen atom with high kinetic energy. The light absorption in ionically dissociated species generates the hydronium radical (H(3)O) and halogen radical (X) within a charge-transfer-to-solvent (CTTS) excitation process. The hydronium radical ultimately decays into a water molecule and hydrogen atom with a characteristic kinetic energy irrespective of the hydrogen halide. We have also investigated the dynamics of an isolated and water-solvated H(3)O radical that we view as a central species in water radiation chemistry. The theoretical findings support the following picture of the HX photochemistry on ice nanoparticles investigated in our molecular beam experiments: HX is acidically dissociated in the ground state on ice nanoparticles, generating the CIP structure, which is then excited by the UV laser light into the CTTS states, followed by the H(3)O radical formation.     

Kinetics and mechanism of the reactions of platinum(II)‐dipicolinate and platinum(II)‐glycylglycine with oxalate ion

The kinetics of the reactions of [Pt(dipic)(H₂O)] and [Pt(digly)(H₂O)] (where H₂dipic = pyridine‐2,6‐dicarboxylic acid and H₂digly = glycylglycine) with oxalate ion were studied at 25°C in aqueous medium by UV–vis spectroscopy at I = 0.1 mol dm^?3 over an wide range of pH. A probable associative pathway may involve a five‐coordinate intermediate leading to the formation of an unidentate oxalate species, which converts to bidentate chelate in subsequent fast steps. The products are isolated and characterized by CHN analysis, IR, and ¹H NMR spectra. The kinetic data from pH variation experiments are fitted by a computer program to a sequence of reactions and the different rate constants are evaluated. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 327–333, 2003