Matrix isolation study of the products of the interaction of electrons and metastable argon atoms with HCCl2F

Two groups of infrared absorptions common to experiments in which samples of HCCl₂ isolated in an argon matrix at 14 K are exposed to vacuum ultraviolet radiation or to electrons produced by ultraviolet irradiation of an alkali metal, as well as to experiments in which the Ar:HCCl₂F sample is codeposited with a beam of argon atoms excited in a microwave discharge, have been assigned to anions produced upon associative and dissociative electron capture by HCCI₂F. Detailed isotopic substitution studies suggest that these anions are (Cl₂C)H?F^?, representing a unique type of hydrogen bonding, and HCCIF^?. The HCClF^? anion photodecomposes in the 345–250nm spectral region, but the products of its photodecomposition have not been identified. Both CCl₂ and Cl₂CF are also produced in the discharge experiments, but there is no evidence for the production of HCF. Mechanisms for the formation of ion products by electron capture and by exposure of HCCl₂F to radiation or to excited argon atoms of energy equal to or less than 11.8 eV are considered.     

Matrix isolation study of the interaction of excited argon atoms with CF2Cl2, CF2ClBr,and CF2Br2. Infrared spectra of the CF2Cl+ and CF2Br+ molecular ions

The infrared absorptions associated with the two CF stretching fundamentals of CF₂Cl⁺ and CF₂Br⁺ have been identified in studies of the matrix-isolated products of the interaction of excited argon atoms with CF₂Cl₂, CF₂ClBr, and CF₂Br₂. The exceptionally high values of the CF stretching frequencies obtained in these experiments are consistent with the implications of previous experimental and theoretical studies.     

Matrix isolation study of the products of the interaction of electrons and of argon atoms in excited Rydberg states with HCCIF2

Infrared absorptions of the (CICF)?H—F^? and HCF^?₂ anions have been identified in the spectrum of the products of the photolysis of HCCIF₂ isolated in an argon matrix at 14 K using radiation in the 147—105 nm spectral range. These anions are also produced in matrix experiments in which the Ar:HCCIF₂ sample is codeposited with an atomic beam of sodium and charge transfer processes are induced by mercury are radiation, as well as in experiments in which the sample is codeposited with a beam of argon that has been passed through a microwave discharge. Both the spectral data and molecular orbital calculations for HCF^?₂ indicate that this molecule has an exceptionally weak CH bond and that its apex angle is considerably more acute than that of the uncharged HCF₂ radical. The high threshold for ion production from HCCIF₂ dictates consideration of the role played by highly excited Rydberg states of argon in the discharge experiments. It appears probable that charge transfer occurs between these excited argon and HCCIF₂. The high ion yield typical of the discharge experiments is also consistent with product formation resulting from collision of matrix-isolated HCCIF₂ with free excitons formed by the impact of highly excited argon atoms at the surface of the solid deposit.     

Matrix isolation study of the vacuum ultraviolet photolysis of allene and methylacetylene. Vibrational and electronic spectra of the species C3, C3H,C3H2, and C3H3

Upon hydrogen-discharge photolysis of normal or deuterium-substituted allene or methylacetylene in an argon or a nitrogen matrix at 14°K, infrared absorptions of all of the C₃H_n species with n < 4 appear. A hydrogen-deformation fundamental of C₃H₂ has been identified in the far infrared. Infrared studies of the partially deuterium- substituted methylacetylenes indicate that extensive photoisomerization occurs. The observed products are consistent with those predicted using the previously postulated gas-phase photolysis mechanism. The ultraviolet spectrum of C₃H₃ corresponds closely with that characteristic of the gas-phase molecule. Comparison of the spectrum between 1900 and 4000 A of photolyzed methylacetylene with that of matrix-isolated graphite vapor has indicated that any new electronic transition of C₃ in this region must be weak.     

Matrix isolation study of the vibrational spectrum and structure of HC2

Detailed isotopic studies of the infrared absorptions characteristic of the products of the decomposition of C₂H₂ in a mild discharge through argon trapped at 14 K indicate that HC₂ is an important product and that an absorption at 3612 cm^?1 can be assigned to the carbon-hydrogen stretching fundamental of this species. The data suffice for determination of the stretching and stretching-interaction force constants of HC₂, which, in turn, have permitted estimates of the bond lengths. The carbon-hydrogen bond is found to be exceptionally strong, and the carbon-carbon bond is intermediate between that characteristic of ground-state C₂ and that of C₂H₂. The estimated rotational spacing is in excellent agreement with that found for HC₂ in recent observations of the interstellar medium.     

The absorption spectra of the phenoxyl radical in solid argon

Vacuum ultraviolet photolysis of phenol, phenol-d₆ and anisole during condensation with excess argon at 20 K has produced and trapped the phenoxyl radical as evidenced by structured absorptions at 397.2 and 628.1 nm. A broad photosensitive 416 ± 2 nm band is tentatively assigned to the phenol cation.     

Evidence for production of the hydroxycarbonyl radical in the decomposition of formic acid on platinum

Formic acid molecules highly diluted in argon were passed through a clean platinum screen at 420–730 K and condensed onto an 8-K CsI window. The well-known decomposition products, CO₂, CO, and H₂O, were observed in the infrared spectra of the resulting matrices. In addition, new absorptions which are attributed to the OCOH free radical were also observed. Experiments with partially deuterated formic acids confirmed that the carbon-hydrogen bond of the formic acid was lost in the formation of the new intermediate species. The activation energy for CO₂ production, E_a = 3.5 ± 0.2 kcal/mol, was determined by monitoring its appearance rate at several different catalyst temperatures.     

Infrared and mass spectral studies of proton irradiated H2O + CO2 ice: Evidence for carbonic acid

The effects of proton irradiation on mixed H₂O + CO₂ (1:1) ices at 20 K were investigated by infrared and mass spectroscopy. Infrared bands due to several radical (HCO, CO₃) and molecular (CO) product species were identified. In addition, several new broad and complex i.r. features were observed. On slow warming, the broad features evolved into a 215–250 K residual film whose absorptions have been tentatively assigned to carbonic acid. This identification agrees with the spectral data for irradiated H₂O + ¹³CO₂ ice and the results of an approximate normal coordinate analysis.     

The infrared matrix isolation spectrum and normal coordinate analysis of the Beryllium Fluoride Dimer

The infrared spectra of the beryllium fluoride vapor species isolated in matrices of neon and argon were obtained in the range (2000–190) cm^?1. Four frequencies were identified as belonging to the dimer Be₂F₄. Assuming the latter to have a planarbridge structure of D_2h symmetry, the frequencies in a neon matrix were tentatively assigned. A normal coordinate analysis of the dimer molecule is presented together with the calculated vibrational frequencies and the calculated mean amplitudes of vibration.     

The reaction of F atoms with C2H4. Vibrational Spectrum of the C2H4F Intermediate trapped in solid argon

When the products of the reaction between F atoms produced in a microwave discharge and C₂H₄ are frozen in a large excess of argon at 14 K, new infrared absorptions appear which can be assigned to the 2-fluoroethyl radical. Studies of the dependence of the product distribution on the F-atom concentration have confirmed that the stabilization of C₂H₄F₂ plays only a minor role under the sampling conditions typical of these experiments. Isotopic substitution experiments have demonstrated that the steric configuration about the CH bond is randomized as a result of the F-atom reaction. Upon irradiation of the sample with the full light of a medium-pressure mercury arc, absorptions of vinyl fluoride and acetylene and of the acetylene—HF complex grow in intensity, while those of FCD₂CH₂ and of FCH₂CD₂ diminish in intensity and those of FCH₂CH₂ a nd of FCH₂CD₂ are unchanged. The F-atom reactions and photolysis processes which occur in these experiments are discussed, and a tunnelling mechanism is proposed to explain the isotopic selectivity in the 2-fluoroethyl photodecomposition. The vibrational spectrum of FCH₂CH₂ is compared with that derived in a recent ab initio calculation.     

Competition between photodissociation and photoionization in methyl iodide

CH₃I has a number of 5pπ → 6p Rydberg states which can be excited by two-photon absorption from the ground state. These two-photon absorptions have been previously detected by molecular ionization with a third photon. They can also be studied by observation of the VUV fluorescence from neutral photofragments (excited iodine atoms) following absorption of a third photon. Similarly it is found that absorption of one photon at 118 nm (10.5 eV) is followed by dissociation into excited iodine atoms as well as ionization. Iodine atom VUV emission is 2–10 times stronger from CD₃I than from CH₃I.     

Thermal Stability of Biodegradable Films Based on Soy Protein and Corn Starch

Summary: In this paper, films were prepared from soy protein and corn starch in different proportions and thermal stability and kinetic parameters were determined through degradation reactions in an inert atmosphere. Solid residues and decomposition products were identified by infrared spectroscopy. Films from corn starch were less thermally stable than soy protein films. The films containing both components had lower thermal stabilities when compared to those of the pure biopolymers. The mechanism of starch thermal degradation seems to occur in a single step, which can be confirmed by the constant E-values during the thermal degradation reaction. For the pure protein and its mixtures an increase in the activation energy was observed during the reaction. Solid residues for protein at different temperatures showed mainly bands related to CO stretching, angular deformation of N H and C H groups. For starch, absorptions related to free and bound O H, CO stretching of CO₂, CO and carbonyl compounds were observed. For the 50/50 mixture bands related to soy protein and corn starch were observed. The gaseous products for soy protein showed absorptions related to CO₂, CO, CO, NH₃ and C H stretching. For pure starch absorptions related to O H stretching from alcohol, CO from CO₂, CO and carbonyl compounds. The 50/50 mixture had the same characteristics as pure soy protein and corn starch.     

Perhydridosilicone films produced by IR laser‐induced chemical vapour deposition from disiloxane

Solid perhydridosilicone films have been produced by transversely excited atmospheric (TEA) and continuous‐wave CO₂ laser‐induced gas‐phase decompositions of H₃SiOSiH₃ controlled by elimination and polymerization of transient silanone H₂SiO and affording silane and hydrogen as side products. The decomposition mechanism is supported by evidence of scavenged intermediates and minor volatile products. The films are characterized by FT infrared and x‐ray photoelectron spectroscopy and by scanning electron microscopy and shown to undergo facile oxidation of the topmost layers in air and chemical changes upon argon ion sputtering. Copyright © 2000 John Wiley & Sons, Ltd.     

Formation of Short Zn−Zn Bonds Stabilized by Simple Cyanide and Isocyanide Ligands

Cyanogen diluted in argon was reacted with laser ablated Zn atoms to produce the NCZnCN and NCZnZnCN cyanides and higher energy isocyanides ZnNC, CNZnNC, and CNZnZnNC, which were isolated in excess argon at 4 K. These reaction products, identified from the matrix infrared spectra of their ‐CN and ‐NC chromophore ligand stretching modes, were confirmed by ¹³C and ¹⁵N isotopic substitution and comparison with frequencies calculated by the B3LYP and CCSD(T) methods using the all electron aug‐cc‐pVTZ basis sets. The cyanide and isocyanide products were increased markedly by mercury arc UV photolysis, which covers the zinc atomic absorption. The above electronic structure calculations that produce appropriate ligand frequencies for these dizinc products also provide their Zn?Zn bond lengths: CCSD(T) calculations find a short 2.367 Å Zn?Zn bond in the NCZnZnCN cyanide, a shorter 2.347 Å Zn?Zn bond in the 37.4 kJ mol^?1 higher energy isocyanide CNZnZnNC, and a longer 4.024 Å bond in the dizinc van der Waals dimer. Thus, the diatomic cyanide (‐CN) and isocyanide (‐NC) ligands are as capable of stabilizing the Zn?Zn bond as many much larger ligands based on their measured and our calculated Zn?Zn bond lengths. This is the first example of dizinc complexes stabilized by different ligand isomers. Additional weaker bands in this region can be assigned to the analogous trizinc molecules NCZnZnZnCN and CNZnZnZnNC.     

Temperature and pressure effects on the far I.R. spectra associated with liquid lattices

The low frequency (10–150 cm^?1) infrared absorptions of selected polar liquids (acetonitrile, t-butyl cyanide, acetone and pivalone) as a function of pressure, temperature and also concentration in a non-polar solvent (CCl₄) have been investigated using a variable-temperature variable-pressure cell, linked with a non-dispersive Michelson interferometer.     

Cyanides and Isocyanides of Zinc,Cadmium and Mercury: Matrix Infrared Spectra and Electronic Structure Calculations for the Linear MNC,NCMCN, CNMNC,NCMMCN, and CNMMNC Molecules

Cadmium atoms from laser ablation react with cyanogen, NC=CN, in excess argon during co-deposition at 4 K, and even more on UV irradiation of the cold samples. Final annealing to 35 K increases bands at 2187.3 and 2089.2 cm⁻¹ at the expense of weaker bands at 2194.6 and 2092.2 cm⁻¹ through addition of another cadmium atom. Reaction products were identified by comparison with B3LYP and CCSD(T) computed frequencies and energies, through frequency differences between Zn and Cd products, and by cyanogen isotopic substitution. The CN radical, ZnNC, and CdNC were observed on sample deposition. Hg arc ultraviolet (UV) irradiation activates the insertion of Cd and Zn to form the NCCdCN, CNCdNC, NCZnCN and CNZnNC molecules. Next annealing increased the dimetal products NCCdCdCN, CNCdCdNC, NCZnZnCN, and CNZnZnNC at the expense of their single metal analogs. Laser ablated mercury amalgam also produced NCHgCN, NCHg−HgCN, CNHgNC and CNHg−HgNC. The Group12 metals form both cyanide and isocyanide products, and the argon matrix also traps the higher energy but much more intensely absorbing isocyanides. In the isocyanide case bond polarity results in very intense infrared absorptions. Group 12 metals produce shorter M−M bonds in the dimetal cyanides NCM−MCN and isocyanides CNM−MNC than in the M−M itself, and their computed M−M bond lengths compare favorably with those measured for dimetal complexes stabilized by large ring containing molecular ligands.     

Formation of Short Zn−Zn Bonds Stabilized by Simple Cyanide and Isocyanide Ligands

Cyanogen diluted in argon was reacted with laser ablated Zn atoms to produce the NCZnCN and NCZnZnCN cyanides and higher energy isocyanides ZnNC, CNZnNC, and CNZnZnNC, which were isolated in excess argon at 4 K. These reaction products, identified from the matrix infrared spectra of their -CN and -NC chromophore ligand stretching modes, were confirmed by ¹³C and ¹⁵N isotopic substitution and comparison with frequencies calculated by the B3LYP and CCSD(T) methods using the all electron aug-cc-pVTZ basis sets. The cyanide and isocyanide products were increased markedly by mercury arc UV photolysis, which covers the zinc atomic absorption. The above electronic structure calculations that produce appropriate ligand frequencies for these dizinc products also provide their Zn−Zn bond lengths: CCSD(T) calculations find a short 2.367 Å Zn−Zn bond in the NCZnZnCN cyanide, a shorter 2.347 Å Zn−Zn bond in the 37.4 kJ mol⁻¹ higher energy isocyanide CNZnZnNC, and a longer 4.024 Å bond in the dizinc van der Waals dimer. Thus, the diatomic cyanide (-CN) and isocyanide (-NC) ligands are as capable of stabilizing the Zn−Zn bond as many much larger ligands based on their measured and our calculated Zn−Zn bond lengths. This is the first example of dizinc complexes stabilized by different ligand isomers. Additional weaker bands in this region can be assigned to the analogous trizinc molecules NCZnZnZnCN and CNZnZnZnNC.     

Matrix Infrared Spectroscopy and Quantum‐Chemical Calculations for the Coinage‐Metal Fluorides: Comparisons of Ar?AuF,Ne?AuF,and Molecules MF2 and MF3

The reactions of laser‐ablated Au, Ag, and Cu atoms with F₂ in excess argon and neon gave new absorptions in the M? F stretching region of their IR spectra, which were assigned to metal‐fluoride species. For gold, a Ng? AuF bond was identified in mixed neon/argon samples. However, this bonding was much weaker with AgF and CuF. Molecules MF₂ and MF₃ (M=Au, Ag, Cu) were identified from the isotopic distribution of the Cu and Ag atoms, comparison of the frequencies for three metal fluorides, and theoretical frequency calculations. The AuF₅ molecule was characterized by its strongest stretching mode and theoretical frequency calculations. Additional evidence was observed for the formation of the Au₂F₆ molecule.     

Infrared laser photoisomerization of 2-fluoroethanol in argon

Different products result from single-photon IR photolysis of 2-fluoroethanol in solid argon depending upon the vibrational mode that is excited. Irradiation of the OH stretch causes an interconversion of the two most stable isomers T₁ and G_g. Irradiation of one CH stretch results in the formation of significant yields of the less stable G₁ and T_g isomers. The isomers of 2-fluoroethanol can be photooriented in argon by IR irradiation.     

(Noble Gas)n-NC+ Molecular Ions in Noble Gas Matrices: Matrix Infrared Spectra and Electronic Structure Calculations

An investigation of pulsed-laser-ablated Zn, Cd and Hg metal atom reactions with HCN under excess argon during co-deposition with laser-ablated Hg atoms from a dental amalgam target also provided Hg emissions capable of photoionization of the CN photo-dissociation product. A new band at 1933.4 cm⁻¹ in the region of the CN and CN⁺ gas-phase fundamental absorptions that appeared upon annealing the matrix to 20 K after sample deposition, and disappeared upon UV photolysis is assigned to (Ar)_nCN⁺, our key finding. It is not possible to determine the n coefficient exactly, but structure calculations suggest that one, two, three or four argon atoms can solvate the CN⁺ cation in an argon matrix with C−N absorptions calculated (B3LYP) to be between 2317.2 and 2319.8 cm⁻¹. Similar bands were observed in solid krypton at 1920.5, in solid xenon at 1935.4 and in solid neon at 1947.8 cm⁻¹. H¹³CN reagent gave an 1892.3 absorption with shift instead, and a 12/13 isotopic frequency ratio–nearly the same as found for ¹³CN⁺ itself in the gas phase and in the argon matrix. The CN⁺ molecular ion serves as a useful infrared probe to examine Ng clusters. The following ion reactions are believed to occur here: the first step upon sample deposition is assisted by a focused pulsed YAG laser, and the second step occurs on sample annealing: (Ar)₂⁺+CN→Ar+CN⁺→(Ar)_nCN⁺.