7 research outputs found
Observation and Characterization of the Hg-O Diatomic Molecule: A Matrix-Isolation and Quantum-Chemical Investigation
Mercuric oxide is a well-known and stable solid, but the diatomic molecule Hg-O is very fragile and do not survive detection in the gas phase. However, laser ablation of Hg atoms from a dental amalgam target into argon or neon containing about 0.3% of 16 O 2 or of 18 O 2 during their condensation into a cryogenic matrix at 4 K allows the formation of O atoms which react on annealing to make ozone and new IR absorptions in solid argon at 521.2 cm â1 for Hg- 16 O or at 496.4 cm â1 for Hg- 18 O with the oxygen isotopic frequency ratio 521.2/496.4 = 1.0500. Solid neon gives a 529.0 cm â1 absorption with a small 7.8 blue shift. CCSD(T) calculations found 594 cm â1 for Hg 16 O and 562 cm â1 for Hg 18 O (frequency ratio = 1.0569). Such calculations usually produce harmonic frequencies that are slightly higher than the anharmonic (observed) values, which supports their relationship. These observed frequencies have the isotopic shift predicted for Hg-O and are within the range of recent high-level frequency calculations for the Hg-O molecule. Spectra for the related mercury superoxide and ozonide species are also observed for the first time
Infrared Spectroscopic and Theoretical Investigations of Group 13 Oxyfluorides OMF2 and OMF (M = B, Al, Ga, In)
Group 13 oxyfluorides OMF2 were produced by the reactions of laser-ablated group 13 atoms M (M = B, Al, Ga and In) with OF2 and isolated in excess neon or argon matrices at 5 K. These molecules were characterized by matrix-isolation infrared spectroscopy and isotopic substitution experiments in conjunction with quantum-chemical calculations. The calculations indicate that the OMF2 molecules have a 2B2 ground state with C2v symmetry. The computed molecular orbitals and spin densities show that the unpaired electron is mainly located at the terminal oxygen atom. Oxo monofluorides OMF were only observed in solid argon matrices and exhibit a linear structure in the singlet ground state. The MâO bonding in the OMF molecules can be rationalized as highly polar multiple bonds based on the calculated bond lengths and natural resonance theory (NRT) analyses. In particular, the molecular orbitals of OBF exhibit the character of a triple bond BâO resulting from two degenerate electron-sharing Ï bonds and a O â B dative Ï bond formed by the oxygen 2p lone pair which donates electron density to the boron empty 2p orbital
Investigation of Molecular Iridium Fluorides IrFn (n=1â6): A Combined Matrix-Isolation and Quantum-Chemical Study
The photo-initiated defluorination of iridium hexafluoride (IrF6) was investigated in neon and argon matrices at 6â
K, and their photoproducts are characterized by IR and UV-vis spectroscopies as well as quantum-chemical calculations. The primary photoproducts obtained after irradiation with λ=365â
nm are iridium pentafluoride (IrF5) and iridium trifluoride (IrF3), while longer irradiation of the same matrix with λ=278â
nm produced iridium tetrafluoride (IrF4) and iridium difluoride (IrF2) by IrâF bond cleavage or F2 elimination. In addition, IrF5 can be reversed to IrF6 by adding a F atom when exposed to blue-light (λ=470â
nm) irradiation. Laser irradiation (λ=266â
nm) of IrF4 also generated IrF6, IrF5, IrF3 and IrF2. Alternatively, molecular binary iridium fluorides IrFn (n=1â6) were produced by co-deposition of laser-ablated iridium atoms with elemental fluorine in excess neon and argon matrices under cryogenic conditions. Computational studies up to scalar relativistic CCSD(T)/triple-ζ level and two-component quasirelativistic DFT computations including spin-orbit coupling effects supported the formation of these products and provided detailed insights into their molecular structures by their characteristic IrâF stretching bands. Compared to the Jahn-Teller effect, the influence of spin-orbit coupling dominates in IrF5, leading to a triplet ground state with C4v symmetry, which was spectroscopically detected in solid argon and neon matrices
(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 1933.4â
cmâ1 in the region of the CN and CN+ gas-phase fundamental absorptions that appeared upon annealing the matrix to 20â
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 CâN absorptions calculated (B3LYP) to be between 2317.2 and 2319.8â
cmâ1. Similar bands were observed in solid krypton at 1920.5, in solid xenon at 1935.4 and in solid neon at 1947.8â
cmâ1. H13CN reagent gave an 1892.3 absorption with shift instead, and a 12/13 isotopic frequency ratioânearly 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++CNâAr+CN+â(Ar)nCN+
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 5â
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 CâN stretches and intense MâH 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
Formation of Hydroxylamine in Low-Temperature Interstellar Model Ices
We irradiated binary
ice mixtures of ammonia (NH<sub>3</sub>) and
oxygen (O<sub>2</sub>) ices at astrophysically relevant temperatures
of 5.5 K with energetic electrons to mimic the energy transfer process
that occurs in the track of galactic cosmic rays. By monitoring the
newly formed molecules <i>online</i> and <i>in situ</i> utilizing
Fourier transform infrared spectroscopy complemented by temperature-programmed
desorption studies with single-photon photoionization reflectron time-of-flight mass
spectrometry, the synthesis of hydroxylamine (NH<sub>2</sub>OH), water
(H<sub>2</sub>O), hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>),
nitrosyl hydride (HNO), and a series of nitrogen oxides (NO, N<sub>2</sub>O, NO<sub>2</sub>, N<sub>2</sub>O<sub>2</sub>, N<sub>2</sub>O<sub>3</sub>) was evident. The synthetic pathway of the newly formed
species, along with their rate constants, is discussed exploiting
the kinetic fitting of the coupled differential equations representing
the decomposition steps in the irradiated ice mixtures. Our studies
suggest the hydroxylamine is likely formed through an insertion mechanism
of suprathermal oxygen into the nitrogenâhydrogen bond of ammonia
at such low temperatures. An isotope-labeled experiment examining
the electron-irradiated D3-ammoniaâoxygen (ND<sub>3</sub>âO<sub>2</sub>) ices was also conducted, which confirmed our findings. This
study provides clear, concise evidence of the formation of hydroxylamine
by irradiation of interstellar analogue ices and can help explain
the question how potential precursors to complex biorelevant molecules
may form in the interstellar medium