Formation of neutral methylcarbamic acid (CH3NHCOOH) and methylammonium methylcarbamate [CH3NH3+][CH3NHCO2-] at low temperature

We study low temperature reactivity of methylamine (CH3NH2) and carbon dioxide (CO2) mixed within different ratios, using FTIR spectroscopy and mass spectrometry. We report experimental evidence that the methylammonium methylcarbamate [CH3NH3(+)][C3NHCO2(-)] and methylcarbamic acid (CH3NHCOOH) are formed when the initial mixture CH3NH2:CO2 is warmed up to temperatures above 40 K. An excess of CH3NH2 favors the carbamate formation while an excess of CO2 leads to a mixture of both methylammonium methylcarbamate and methylcarbamic acid. Quantum calculations show that methylcarbamic acid molecules are associated into centrosymmetric dimers. Above 230 K, the carbamate breaks down into CH3NH2 and CH3NHCOOH, then this latter dissociates into CH3NH2 and CO2. After 260 K, it remains on the substrate a solid residue made of a well-organized structure coming from the association between the remaining methylcarbamic acid dimers. This study shows that amines can react at low temperature in interstellar ices rich in carbon dioxide which are a privileged place of complex molecules formation, before being later released into "hot core" regions.     

Infrared spectra of CH(3)-MoH, CH(2)=MoH(2), and CH(triple bond)MoH(3) formed by activation of CH(4) by molybdenum atoms

Reaction of laser-ablated Mo atoms with CH(4) in excess argon forms the CH(3)-MoH, CH(2)=MoH(2), and CH(triple bond)MoH(3) molecules, which are identified from infrared spectra by isotopic substitution and density functional theory frequency calculations. These simple methyl, methylidene, and methylidyne molybdenum hydride molecules are reversibly interconverted by alpha-H transfers upon visible and ultraviolet irradiations. The methylidene dihydride CH(2)=MoH(2) exhibits CH(2) and MoH(2) distortion and agostic interaction to a lesser degree than CH(2)=ZrH(2). Molybdenum methylidyne trihydride CH(triple bond)MoH(3) is a stable C(3v) symmetry molecule.     

Interstellar Enolization-Acetaldehyde (CH3CHO) and Vinyl Alcohol (H2CCH(OH)) as a Case Study

Owing to the unique conditions in cold molecular clouds, enols—the thermodynamically less stable tautomers of aldehydes and ketones—do not undergo tautomerization to their more stable tautomers in the gas phase because they cannot overcome tautomerization barriers at the low temperatures. Laboratory studies of interstellar analog ices have demonstrated the formation of several keto–enol tautomer pairs in astrochemically relevant ice mixtures over the last years. However, so far only one of them, acetaldehyde−vinyl alcohol, has been detected in deep space. Due to their reactivity with electrophiles, enols can play a crucial role in our understanding of the molecular complexity in the interstellar medium and in comets and meteorites. To study the enolization of aldehydes in interstellar ices by interaction with galactic cosmic rays (GCRs), we irradiated acetaldehyde ices with energetic electrons as proxies of secondary electrons generated in the track of GCRs while penetrating interstellar ices. The results indicate that GCRs can induce enolization of acetaldehyde and that intra- as well as intermolecular processes are relevant. Therefore, enols should be ubiquitous in the interstellar medium and could be searched for using radio telescopes such as ALMA. Once enols are detected and abundances are established, they can serve as tracers for the non-equilibrium chemistry in interstellar ices thus eventually constraining fundamental reaction mechanisms deep inside interstellar ices.     

Synthesis, structure, and magnetic properties of [(S)-[PhCH(CH3)N(CH3)3]][Mn(CH3CN)2/3Cr(ox)3] x (CH3CN)_(solvate), a 2D chiral magnet containing a quaternary ammonium chiral cation

The synthesis, structure, and magnetic properties of a novel oxalate-based bimetallic magnet obtained by using the chiral (S)-trimethyl-(1-phenyl-ethyl)-ammonium, ((S)-[PhCH(CH3)N(CH3)3](+)), cation as template is reported. This compound can be formulated as [(S)-[PhCH(CH3)N(CH3)3]][Mn(CH3CN)2/3Cr(ox)3] x (CH3CN)_(solvate), and it crystallizes in the chiral trigonal space group P3. It shows a distorted two-dimensional honeycomb structure formed by Mn(II) and Cr(III) ions connected through oxalate anions with [(S)-[PhCH(CH3)N(CH3)3](+) cations and solvent molecules intercalated between the oxalate layers. Two-thirds of the Mn(II) ions of the honeycomb anionic network are heptacoordinated. This compound behaves as a soft ferromagnet with an ordering temperature of 5.6 K.     

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.     

Interdependence of redox state,hydrogen bonding,anion recognition and charge partition in crystals of (EDT-TTF-CONHMe)6 [Re6Se8(CN)6] (CH3CN)2(CH2Cl2)2

Neutral pi-conjugated molecules and their radical cations co-exist in [(EDT-TTF-CONHMe+*)4(EDT-TTF-CONHMe0)2] [Re6Se8(CN)6]4- (CH3CN)2(CH2Cl2)2 whose crystal structure reveals that, upon one-electron oxidation, an activation of the N-H and C-H hydrogen bond donor ability is coupled to a deactivation of the hydrogen bond acceptor character of the carbonyl oxygen atom: this is expressed in the supramolecular hydrogen bond pattern and, ultimately, into charge localisation and partition in the solid state.     

二(三苯基膦)水杨酸铜(Ⅰ)乙醇溶剂配合物的晶体结构

The crystal and molecular structure of [ (PPh3)2Cu(O2CPhOH)] @ CH3CH2OH has been determined by X-raycrystallography. It crystallizes in the monoclinic system, space group P21/c, with Mr = 771.26 (C45H41CuO4P2),a = 0. 96413(19) nm, b= 1. 5780(3) nm, c = 2. 5426(5) nm, β = 100. 27(3)°, V= 3. 8065(13) nm3, The titlecompound consists of discrete copper (Ⅰ) bis(triphenylphosphine) salicylate molecules and ethanol solvate. EachCu is coordinated to two phosphorus atoms of triphenylphosphine ligands and one of carboxylate oxygens in a trigonalplanar geometry. In the solid, the intramolecular hydrogen bond and extensive intermolecular interaction connecting(PPh3) 2Cu(O2CPhOH) molecules and ethanol solvate form hydrogen bonds network which stabilize the crystalstructure.     

Infrared photodissociation spectroscopy of Al(+)(CH(3)OH)(n) (n = 1-4)

Infrared photodissociation spectra of Al(+)(CH(3)OH)(n) (n = 1-4) and Al(+)(CH(3)OH)(n)-Ar (n = 1-3) were measured in the OH stretching region, 3000-3800 cm(-1). For n = 1 and 2, sharp absorption bands were observed in the free OH stretching region, all of which were well reproduced by the spectra calculated for the solvated-type geometry with no hydrogen bond. For n = 3 and 4, there were broad vibrational bands in the energy region of hydrogen-bonded OH stretching vibrations, 3000-3500 cm(-1). Energies of possible isomers for the Al(+)(CH(3)OH)(3),4 ions with hydrogen bonds were calculated in order to assign these bands. It was found that the third and fourth methanol molecules form hydrogen bonds with methanol molecules in the first solvation shell, rather than a direct bonding with the Al(+) ion. For the Al(+)(CH(3)OH)(n) clusters with n = 1-4, we obtained no evidence of the insertion reaction, which occurs in Al(+)(H(2)O)(n). One possible explanation of the difference between these two systems is that the potential energy barriers between the solvated and inserted isomers in the Al(+)(CH(3)OH)(n) system is too high to form the inserted-type isomers.     

Theoretical study of the reactions CF3CH2OCHF2 + OH/Cl and its product radicals and parent ether(CH3CH2OCH3) with OH

A dual-level direct dynamic method is employed to study the reaction mechanisms of CF3CH2OCHF2 (HFE-245fa2; HFE-245mf) with the OH radicals and Cl atoms. Two hydrogen abstraction channels and two displacement processes are found for each reaction. For further study, the reaction mechanisms of its products (CF3CH2OCF2 and CF3CHOCHF2) and parent ether CH3CH2OCH3 with OH radical are investigated theoretically. The geometries and frequencies of all the stationary points and the minimum energy paths (MEPs) are calculated at the B3LYP/6-311G(d,p) level. The energetic information along the MEPs is further refined at the G3(MP2) level of theory. For reactions CF3CH2OCHF2 + OH/Cl, the calculation indicates that the hydrogen abstraction from --CH2-- group is the dominant reaction channel, and the displacement processes may be negligible because of the high barriers. The standard enthalpies of formation for the reactant CF3CH2OCHF2, and two products CF3CH2OCHF2 and CF3CHOCHF2 are evaluated via group-balanced isodesmic reactions. The rate constants of reactions CF3CH2OCHF2 + OH/Cl and CH3CH2OCH3 + OH are estimated by using the variational transition state theory over a wide range of temperature (200-2000 K). The agreement between the theoretical and experimental rate constants is good in the measured temperature range. From the comparison between the rate constants of the reactions CF3CH2OCHF2 and CH3CH2OCH3 with OH, it is shown that the fluorine substitution decreases the reactivity of the C--H bond.     

A Photoionization Study on the Detection of 1-Sila Glycolaldehyde (HSiOCH2OH), 2-Sila Acetic Acid (H3SiCOOH), and 1,2-Disila Acetaldehyde (HSiOSiH3)

The identification of silicon-substituted, complex organics carrying multiple functional groups by classical infrared spectroscopy is challenging because the group frequencies of functional groups often overlap. Photoionization (PI) reflectron time-of-fight mass spectrometry (ReTOF-MS) in combination with temperature-programmed desorption (TPD) holds certain advantages because molecules are identified after sublimation from the matrix into in the gas phase based on distinct ionization energies and sublimation temperatures. In this study, we reveal the detection of 1-silaglycolaldehyde (HSiOCH₂OH), 2-sila-acetic acid (H₃SiCOOH), and 1,2-disila-acetaldehyde (H₃SiSiHO)—the silicon analogues of the well-known glycolaldehyde (HCOCH₂OH), acetic acid (H₃CCOOH), and acetaldehyde (H₃CCHO), in the gas phase after preparation in silane (SiH₄)–carbon dioxide ices exposed to energetic electrons and subliming the neutral reaction products formed within the ices into the gas phase.     

Theoretical investigation on the replacement of CH groups by N atoms in caged structure (CH)8

A molecular design was performed for the caged molecule (CH)8: the replacement of CH groups by N atoms to increase the content of N as well as reduce the content of H. A series of caged molecules were obtained: (CH)xN(8-x) (0 < or = n < or = 8). The studied aspects are as follows: (i) molecular geometries and electronic structures, (ii) the analysis of the electronic structure using natural bond orbital (NBO) and atoms in molecules (AIM), and (iii) some physicochemical properties of studied molecules, such as the dipole moments, IR vibrational spectra, NMR chemical shifts, heats of formation, and relative specific impulses, were provided. Our studies show that these molecules should be a kind of potential and novel energetic material. Our work provides some useful information for the experimental study of these molecules. The effect of the substitution of N atoms for CH groups on the properties of this kind of caged molecule is presented.     

Photolysis of CH3C(O)CH3 (248 nm, 266 nm), CH3C(O)C2H5 (248 nm) and CH3C(O)Br (248 nm): pressure dependent quantum yields of CH3 formation

The formation of CH(3) in the 248 or 266 nm photolysis of acetone (CH(3)C(O)CH(3)), 2-butanone (methylethylketone, MEK, CH(3)C(O)C(2)H(5)) and acetyl bromide (CH(3)C(O)Br) was examined using the pulsed photolytic generation of the radical and its detection by transient absorption spectroscopy at 216.4 nm. Experiments were carried out at room temperature (298 +/- 3 K) and at pressures between approximately 5 and 1500 Torr N(2). Quantum yields for CH(3) formation were derived relative to CH(3)I photolysis at the same wavelength in back-to-back experiments. For acetone at 248 nm, the yield of CH(3) was greater than unity at low pressures (1.42 +/- 0.15 extrapolated to zero pressure) confirming that a substantial fraction of the CH(3)CO co-product can dissociate to CH(3) + CO under these conditions. At pressures close to atmospheric the quantum yield approached unity, indicative of almost complete collisional relaxation of the CH(3)CO radical. Measurements of increasing CH(3)CO yield with pressure confirmed this. Contrasting results were obtained at 266 nm, where the yields of CH(3) (and CH(3)CO) were close to unity (0.93 +/- 0.1) and independent of pressure, strongly suggesting that nascent CH(3)CO is insufficiently activated to decompose on the time scales of these experiments at 298 K. In the 248 nm photolysis of CH(3)C(O)Br, CH(3) was observed with a pressure independent quantum yield of 0.92 +/- 0.1 and CH(3)CO remained below the detection limit, suggesting that CH(3)CO generated from CH(3)COBr photolysis at 248 nm is too highly activated to be quenched by collision. Similar to CH(3)C(O)CH(3), the photolysis of CH(3)C(O)C(2)H(5) at 248 nm revealed pressure dependent yields of CH(3), decreasing from 0.45 at zero pressure to 0.19 at pressures greater than 1000 Torr with a concomitant increase in the CH(3)CO yield. As part of this study, the absorption cross section of CH(3) at 216.4 nm (instrumental resolution of 0.5 nm) was measured to be (4.27 +/- 0.2) x 10(-17) cm(2) molecule(-1) and that of C(2)H(5) at 222 nm was (2.5 +/- 0.6) x 10(-18) cm(2) molecule(-1). An absorption spectrum of gas-phase CH(3)C(O)Br (210-305 nm) is also reported for the first time.     

Metastable decompositions of gem-dialkoxyalkanes upon electron impact. III. Diethoxymethane (CH(2)(OCH(2)CH(3))(2))

Unimolecular metastable decomposition of diethoxymethane (CH(2)(OCH(2)CH(3))(2), 1) upon electron impact has been investigated by means of mass-analyzed ion kinetic energy (MIKE) spectrometry and theD-labeling technique in conjunction with thermochemistry. The m/z 103 ion ([M - H](+) : CH(OCH(2)CH(3)) = O(+)CH(2)CH(3)) decomposes into the m/z 47 ion (protonated formic acid, CH(OH) = O(+)H) by consecutive losses of two C(2)H(4) molecules via an m/z 75 ion. The resulting product ion at m/z 47 further decomposes into the m/z 29 and 19 ions by losses of H(2)O and CO, respectively, via an 1,3-hydroxyl hydrogen transfer, accompanied by small kinetic energy release (KER) values of 1.3 and 18.8 meV, respectively. When these two elimination reactions are suppressed by a large isotope effect, however, another 1,1-H(2)O elimination with a large KER value (518 meV) is revealed. The m/z 89 ion ([M - CH(3)](+) : CH(2)(OCH(2)CH(3))O(+) = CH(2)) decomposes into the m/z 59 ion (CH(3)CH(2)O(+) = CH(2)) by losing CH(2)O in the metastable time window. The source-generated m/z 59 ion ([M - OCH(2)CH(3)](+) : CH(2) = O(+)CH(2)CH(3)) decomposes into the m/z 41 (CH(2) = CH(+)CH(2)) and m/z 31 (CH(2) = O(+)H) ions by losses of H(2)O and C(2)H(4), respectively, with considerable hydrogen scrambling prior to decomposition. Copyright 2000 John Wiley & Sons, Ltd.     

Theoretical study on the reaction CX3 + SiH(CH3)3 (X = H, F)

Theoretical investigations are carried out on the multiple-channel reactions, CH(3) + SiH(CH(3))(3) → products and CF(3) + SiH(CH(3))(3) → products. The minimum energy paths (MEP) are calculated at the MP2/6-311 + G(d,p) level, and energetic information is further refined by the MC-QCISD (single point) method. The rate constants for major reaction channels are calculated by the canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) correction over the temperature range 200-1500 K. The theoretical rate constants are in good agreement with the available experimental data and are found to be k(1a)(T) = 1.93 × 10(-24) T(3.15) exp(-1214.59/T) and k(2a)(T) = 1.33 × 10(-25) T(4.13) exp(-397.94/T) (in unit of cm(3) molecule(-1) s(-1)). Our calculations indicate that hydrogen abstraction channel from SiH group is the major channel due to the smaller barrier height among five channels considered.     

Reactions of CH3SH and (CH3)2S2 on the (0001) and (000) Surfaces of ZnO

Temperature-programmed desorption (TPD) was used to study the adsorption and reaction of CH3SH and (CH3)2S2 on the (0001) and (000) surfaces of ZnO. The interaction of these molecules with ZnO was found to be structure-sensitive. Both CH3SH and (CH3)2S2 adsorb dissociatively on ZnO(0001), forming adsorbed methylthiolate intermediates and only molecularly on ZnO(000). In the case of CH3SH, this result is consistent with that reported previously for the interaction of Br?nsted acids with ZnO and indicates that exposed cation-anion pairs are the active sites for dissociative adsorption. Only exposed Zn cations are required for the dissociative adsorption of (CH3)2S2. Methylthiolate species produced by dissociative adsorption of CH3SH and (CH3)2S2 on ZnO(0001) were found to undergo a variety of reaction pathways, including coupling to produce dimethyl sulfide and oxidation to formaldehyde, CO, and CO2. Pathways for the production of these various products are proposed.     

Computational study of the reaction of CH2(X3B1) with CH3OH

The reaction of triplet methylene with methanol is a key process in alcohol combustion but surprisingly this reaction has never been studied. The reaction mechanism is investigated by using various high-level ab initio methods, including the complete basis set extrapolation (CBS-QB3 and CBS-APNO), the latest Gaussian-n composite method (G4), and the Weizmann-1 method (W1U). A total of five product channels and six transition states are found. The dominant mechanism is direct hydrogen abstraction, and the major product channel is CH(3) + CH(3)O, involving a weak prereactive complex and a 7.4 kcal/mol barrier. The other hydrogen abstraction channel, CH(3) + CH(2)OH, is less important even though it is more exothermic and involves a similar barrier height. The rate coefficients are predicted in the temperature range 200-3000 K. The tunneling effect and the hindered internal rotational freedoms play a key role in the reaction. Moreover, the reaction shows significant kinetic isotope effect.     

Hot filament-dissociation of (CH3)3SiH and (CH3)4Si, probed by vacuum ultra violet laser time of flight mass spectroscopy

The decomposition of trimethylsilane and tetramethylsilane has been investigated for the first time, using hot wire (catalytic) at various temperatures. Trimethylsilane is catalytic-dissociated in these species SiH(2), CH(3)SiH, CH(3), CH(2)Si. Time of flight mass spectroscopy signal of these species are linearly increasing with increasing catalytic-temperature. Time of flight mass spectroscopy (TOFMS) signals of (CH(3))(3)SiH and photodissociated into (CH(3))(2)SiH are decreasing with increasing hot filament temperature. TOFMS signal of (CH(3))(4)Si is decreasing with increasing hot wire temperature, but (CH(3))(3)Si signal is almost constant with increasing the temperature. We calculated activation energies of dissociated species of the parental molecules for fundamental information of reaction kinetics for the first time. Catalytic-dissociation of trimethylsilane, and tetramethylsilane single source time of flight coupled single photon VUV (118 nm) photoionization collisionless radicals at temperature range of tungsten filament 800-2360 K. The study is focused to understand the fundamental information on reaction kinetics of these molecules at hot wire temperature, and processes of catalytic-chemical vapour deposition (Cat-CVD) technique which could be implemented in amorphous and crystalline SiC semiconductors thin films.     

A Photoionization Reflectron Time-of-Flight Mass Spectrometric Study on the Detection of Ethynamine (HCCNH2) and 2H-Azirine (c-H2CCHN)

Ices of acetylene (C₂H₂) and ammonia (NH₃) were irradiated with energetic electrons to simulate interstellar ices processed by galactic cosmic rays in order to investigate the formation of C₂H₃N isomers. Supported by quantum chemical calculations, experiments detected product molecules as they sublime from the ices using photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS). Isotopically-labeled ices confirmed the C₂H₃N assignments while photon energies of 8.81 eV, 9.80 eV, and 10.49 eV were utilized to discriminate isomers based on their known ionization energies. Results indicate the formation of ethynamine (HCCNH₂) and 2H-azirine (c-H₂CCHN) in the irradiated C₂H₂:NH₃ ices, and the energetics of their formation mechanisms are discussed. These findings suggest that these two isomers can form in interstellar ices and, upon sublimation during the hot core phase, could be detected using radio astronomy.     

Mechanistical studies on the formation of isotopomers of hydrogen peroxide (HOOH), hydrotrioxy (HOOO), and dihydrogentrioxide (HOOOH) in electron-irradiated H(2)(18)O/O(2) ice mixtures

In order to investigate the chemical reactions inside water-oxygen ice mixtures in extreme environments, and to confirm the proposed reaction mechanisms in pure water ice, we conducted a detailed infrared spectroscopy and mass spectrometry study on the electron irradiation of H(2)(18)O/O(2) ice mixtures. The formation of molecular hydrogen, isotopically substituted oxygen molecules (18)O(18)O and (16)O(18)O, ozone ((16)O(16)O(16)O, (16)O(16)O(18)O, and (16)O(18)O(16)O), hydrogen peroxide (H(18)O(18)OH, H(16)O(16)OH and H(16)O(18)OH), hydrotrioxy (HOOO), and dihydrogentrioxide (HOOOH) were detected. Kinetic models and reaction mechanisms are proposed to form these molecules in water and oxygen-rich solar system ices.     

Experimental infrared spectra of Cl-(ROH) (R = H, CH3, CH3CH2) complexes in the gas-phase

Infrared multiple photon dissociation spectra for the chloride ion solvated by either water, methanol or ethanol have been recorded using an FTICR spectrometer coupled to a free-electron laser, and are presented here along with assignments to the observed bands. The assignments made to the Cl(-)/H(2)O, Cl(-)(CH(3)OH), and Cl(-)(CH(3)CH(2)OH) spectra are based on comparison with the neutral H(2)O, CH(3)OH, and CH(3)CH(2)OH spectra, respectively. This work confirms that a band observed around 1400 cm(-1) in the Cl(-)(H(2)O) spectrum is not due to the Ar tag in Ar predissociation spectra. The carrier of this band is, most likely, the first overtone of the OHCl bend. Based on the position of the overtone in the IRMPD spectrum, 1375 cm(-1), the fundamental must occur very close to 700 cm(-1) and observation of this band should aid theoretical treatments of the spectrum of this complex. B3LYP/6-311++G(2df,2pd) calculations are shown to reproduce the IRMPD spectra of all three solvated chloride species. They also predict that attaching one or two Ar atoms to the Cl(-)(H(2)O) complex results in a shift of no more than a few wavenumbers in the fundamental bands for the bare complex, in agreement with previous experiment. For both alcohol-Cl(-) complexes, the S(N)2 "backside attack" isomers are not observed and Cl(-) is predicted theoretically, and confirmed experimentally, to be bound to the hydroxyl hydrogen. For Cl(-)(CH(3)CH(2)OH), the trans and gauche conformers are similar in energy, with the gauche conformer predicted to be thermodynamically favoured. The experimental infrared spectrum agrees well with that predicted for the gauche conformer but a mixture of gauche and anti conformers cannot be ruled out based on the experimental spectra nor on the computed thermochemistry.