Solid Argon Matrices Research Articles

Resonance Raman spectra of the transient Cl − and Br − radical anions

The resonance Raman spectra of the short-lived radical anions Cl ▪ 2 − and Br ▪ − in aqueous solution are reported. The observed wavenumbers of 279 cm −1 for Cl ▪ − and 177 cm −1 for Br ▪ − are about 10% higher than those published for the corresponding species isolated in solid argon matrices. Under the assumption of a Morse potential. harmonic frequencies and anharmonicity constants are calculated to be 286.4 and 3.83 cm −1 for Cl ▪ − and 187.2 and 5.17 cm −1 for Br ▪ −. These values lead to extrapolated dissociation energies of 0.66 and 0.21 eV, respectively. These results are compared with those from matrix-isolation studies at low temperatures and work in the gas phase.

Fluorescence from the a 5P and a 3P states of matrix-isolated Fe atoms

Tunable dye laser radiation has been used to examine the a 5P - a 5D and a 3P - a 5D transitions of the Fe atom isolated in solid argon and solid krypton matrices. In the solid argon case the excitation spectrum profile indicates that the 5P 3 state has at least two components separated by 37 cm −1. Excitation from the 5D 4 ground state to 5P 2 involves relaxation to the 5P 3 level before emission. Pumping into the 3P 2 state results in fluorescent transitions from the 5P 3 level as well as from 3P 2.

Studies of the reactions of lithium atoms with methyl cyanide and methyl isocyanide in inert gas matrices

Linear LiNC is known to be the more stable isomer when isolated in inert gas matrices at low temperatures (4–15K). 1 In an attempt to form the other geometrical isomer, LiCN, studies of the reaction of lithium atoms with CH 3CN and CH 3NC were undertaken. A new absorption in the CN stretching region was observed when lithium atoms were co-condensed with CH 3NC in solid argon and xenon matrices. Photolysis of the matrices with a medium pressure Hg lamp during deposition of Li/CH 3NC seemed to favour the formation of the more stable isomer, LiNC. Reactions of lithium atoms with CH 3CN only led to the formation of LiNC, with or without photolysis.

Visible and near-infrared fluorescence spectra of Fe atoms in argon matrices

Argon laser and dye laser excitations of Fe atoms at dilute concentrations in solid argon matrices gave rise to about 50 fluorescence bands spanning the region from 24 600–11 300 cm−1. Most of the bands have half-widths of 3–10 cm−1. The bands all correspond to transitions terminating in levels of either the a 5D or the a 5F quintet. Spacings of the levels within these two multiplets are the same in the matrix as in the gaseous atom. The fluorescence band peak intensities to the red of the laser line vary as the first power of the laser intensity. The peak intensities of fluorescence bands to the blue of the laser excitation vary as about the 1.2 power of the laser intensity and are significantly dependent upon matrix concentration.

Dititanium and divanadium

The Ar+ laser-excited spectrum of matrix-isolated V2 consists of a resonance Raman progression with ωe=537.5 cm−1 and ωexe=4.2 cm−1. With increasing laser power several members of an anti-Stokes progression and sequence components on both Stokes and anti-Stokes members of this progression were observed and attributed to transitions originating from vibrationally excited stated populated as a result of laser irradiation. A second system with ωe=508 and ωexe=3.3 cm−1 also grew in with increasing laser power and 496.5 nm excitation. This was interpreted as a resonance Raman progression within an electronically excited state (A) of V2. The electronic resonance Raman spectrum corresponding to the A→X transition was also observed as well as one to another low-lying electronic excited state. The v′=0 level of state A was found to lie 1860 cm−1 above the v″=0 level of the ground state. The multiple photon nature of the transitions discussed above was determined by performing laser power measurements. The resonance Raman spectrum of Ti2 was excited with HeNe and dye laser illumination in solid argon matrices containing titanium. As with V2, laser irradiation populated excited vibrational states of the ground state, producing an anti-stokes, resonance Raman progression. Isotopic components of Ti2 were resolvable under high resolution, corroborating the assignment. A discussion of multiple bonding in transition metal dimers is presented which shows that the contribution of bonds originating from the atomic d orbitals do not always contribute uniformly to the metal–metal force constant. Hence the formal bond order is not always a good gauge of the bond strength of a transition metal dimer.

Absorption and emission spectra of matrix-isolated GeTe

Abstract Systems of broad bands have been observed in the absorption and laser-induced emission spectra of the GeTe molecule in solid argon and krypton matrices. Hitherto unreported electronic states have been characterized: a , ν 00 = 15 500 cm −1 ; B , ν 00 = 20 070, ω e = 190 cm −1 ; C , ν 00 = 23 500, ω e = 270 cm −1 . Higher energy states are also reported as well as an emission system in the red which is probably due to the Ge 2 Te 2 .

High-temperature generation and ESR matrix isolation studies of ZnF and CdF in neon and argon matrices

The diatomic radicals, ZnF and CdF, have been generated at high temperatures and isolated in solid neon and argon matrices at 4 K and 12 K, respectively. ESR studies of these 2 Σ ground-state radicals yield the following parameters: ZnF, g ⊥ = 1.996(1), g ⊥ = 2.002(1), A ⊥( 19 F) = 143(2) MHz, A ‖( 19F) = 673(2) MHz ; CdF, g ⊥ = 1.985(2), g ‖ = 2.001(3), A ⊥ = 64(2), A ‖ = 670(7). The relationship between metal ionization potentials and 19F hfs is discussed and compared to other diatomic radical species. ZnF and CdF exhibit the most extreme degree of preferential orientation in the neon matrix lattice observed thus far.

A search for the infrared fundamental of matrix-isolated XeF

Various xenon/fluorine mixtures were photolyzed in solid argon matrices and examined in the infrared spectral region with either a Fourier transform spectrometer or with a grating spectrometer. After photolysis, a strong peak was observed at 215 cm−1 in addition to the known XeF2(ν3) peak at 549 cm−1. The appearance of the same two bands in Ar matrices containing the vapors over XeF2 indicated the assignment of the 215 cm−1 band to XeF2(ν2). The fundamental of XeF was not observed either because it is masked by the XeF2(ν2) peak or because it has a small infrared absorption coefficient.

ESR of the BS Molecule in Inert Matrices at 4°K

ESR spectra of 11BS and 10BS molecules in their ground 2Σ+ states were measured while isolated in solid neon and argon matrices at 4°K. g tensors and hyperfine structure constants for interaction with 11B and 10B were determined. In neon the magnetic parameters for BS are g∥11=2.0016(1), g⊥=1.9942(1), A∥(11B)= 853.3(3) MHz, and A⊥ (11B)=766.7(3) MHz. Observation of weak ESR signals attributed to 33S hfs yields | A⊥ (33S)|=16 (2) MHz. The observed Δ g⊥ is in excellent accord with the magnitude and sign of the spin-doubling constant, γo, as derived from published gas phase optical data. A CNDO calculation of the ground state wavefunction for BS was made and used to compare calculated spin densities and g values with experimental values. A comparison of the chemical bonding in BS and BO is given.

Laser-Excited Vibrational Fluorescence of Matrix-Isolated Carbon Monoxide

The infrared emission of CO molecules isolated in solid neon and argon matrices has been observed at very low temperature. The optical excitation of carbon monoxide was provided by a $Q$-switched frequency-doubled C${\mathrm{O}}_{2}$ laser. The fluorescence lifetime ${\ensuremath{\tau}}_{F}$ was found to lie in the range 4-8 msec, with no appreciable change of ${\ensuremath{\tau}}_{F}$ as the matrix/reactant ratio increased from 100 to 1000. On the other hand, a strong dependence of ${\ensuremath{\tau}}_{F}$ with temperature has been observed.

Matrix isolation studies of methyl cyanide and methyl isocyanide in solid argon

The i.r. spectra of CH 3CN, CD 3CN, CH 3NC, CD 3NC and CH 3N 13C have been investigated in solid argon matrices at 20°K. The spectra of the monomeric species indicate that the matrix environment removes the degeneracy of the E modes. Absorption features attributed to the pure and mixed dimer species and force constant calculations support an antiparallel alignment of the molecules in the dimer in which the interaction is through the CN or NC groups.

ESR and Optical Spectra of the ScS and YS Molecules

ESR spectra of the ScS and YS molecules in their ground 2Σ+ states were measured while trapped in solid argon or neon matrices at 4°K. g tensors and hyperfine structure constants for interaction with the metal nuclei were accurately derived, within the ambiguity of multiple matrix sites. Earlier ESR data on ScO were also more accurately analyzed, and a comparison is given of the magnetic parameters for the diatomic oxide and sulfide molecules of Sc, Y, and La. The ir spectra of ScS and YS in argon matrices yielded bands at 554 and 483 cm−1, respectively, and the A 2Π← X 2Σ transition of YS was observed at 7300 Å.

Nuclear gamma resonance studies on matrix-isolated FeCl 2 molecules at 4.2°K

A study of the Mössbauer effect of FeCl 2 in solid argon and xenon matrices at 4.2°K gives for the monomer a quadrupole splitting = 0.62 ± 0.05 mm/sec and an isomer shift = 0.88 ± 0.05 mm/sec with respect to Fe metal at 300°K. In a xenon matrix the FeCl 2 molecules appear to be distributed between two different sites, one of which can be removed by annealing the matrix at 42°K.

Hyperfine Interaction and Chemical Bonding in the BeH Molecule

ESR spectra of the BeH and BeD molecules in their ground 2Σ+ states were measured while isolated in solid argon matrices at 4°K. g tensors and hyperfine structure (hfs) constants for interaction with 9Be, H, and D were determined. |Ψ (0)|2 values at Be and H nuclei were found to be 0.317(2) and 0.0434(2) a.u., respectively, as compared to 0.3223 and 0.0367 a.u. recently calculated by Bender and Davidson using a 1039 CI wavefunction. The HF SCF function of Cade and Huo gave poorer agreement with the measured |Ψ (0)|N2 values but gave satisfactory agreement with experimental values of 〈(3 cos2θN−1)/rN3〉. Approximate spin distributions and bonding among the alkaline-earth hydride molecules are briefly discussed.

Geometry and Infrared Spectra of Matrix-Isolated Rare-Earth Halides. I. LaF3, CeF3, PrF3, NdF3, SmF3, and EuF3

The infrared absorption spectra (40–800 cm−1) of the trifluorides of lanthanum, cerium, praseodymium, neodymium, samarium, and europium isolated in solid argon, krypton, and nitrogen matrices have been obtained. For LaF3, CeF3, SmF3, and EuF3 only the asymmetric stretching mode and the bending modes were observed; these molecules are assigned a planar configuration. For PrF3 the symmetric and asymmetric stretching modes were observed together with the bending modes; PrF3 is accordingly assigned a pyramidal configuration. At present the spectrum of NdF3 cannot be satisfactorily interpreted, but a number of possibilities are explored. Using a valence force field approximation, force constants have been derived from the measured fundamental frequencies and the infrared-inactive symmetric stretching frequency of the planar molecules has been estimated. Statistical entropies have also been calculated from the vibrational data and molecular geometries and are compared with third-law values.

Hyperfine Interaction, Chemical Bonding, and Isotope Effect in ZnH, CdH, and HgH Molecules

ESR spectra of ZnH, CdH, HgH, and HgD molecules in their ground Σ+2 states were measured while trapped in solid argon matrices at 4°K. g tensors and hyperfine structure (hfs) constants for interaction with H, D, 111,113Cd, and 199,201Hg nuclei were observed. Coefficients of approximate LCAO wavefunctions are derived from these magnetic parameters and correlated with chemical bonding trends in the series and with the limiting united-atom model. Replacing H by D in HgH causes an increase of spin density on Hg and a decrease in g∇. This is shown to be largely due to the small decrease in interatomic distance and is discussed relative to other spectroscopic observations.

Hyperfine Interaction and Chemical Bonding in MgH, CaH, SrH, and BaH Molecules

ESR spectra of MgH, CaH, SrH, and BaH molecules in their ground Σ+2 states were measured while isolated in solid argon matrices at 4°K. The molecules were prepared by quenching metal and hydrogen atom beams in a stream of argon. g tensors and hyperfine structure (hfs) constants for interaction with H, and in the case of MgH, with 25Mg and D, were determined. For 25MgH, | Ψ (0) |2 at Mg and H nuclei were found to be 0.800(8) and 0.0663(2) a.u., respectively, in good agreement with 0.7635 and 0.03789 a.u. recently calculated by Chan and Davidson using a 953 CI wavefunction. It is evident that such elaborate calculations are necessary to obtain accurate theoretical spin densities. Hydrogen hf interaction within the group of molecules indicate less ionicity than in the corresponding diatomic fluorides although the spin density is still predominantly on the metal atoms. Metal p and d contributions are approximately derived from the observed Δg⊥ values and discussed in relation to the united-atom model.

Hyperfine Interaction and Chemical Bonding in MgF, CaF, SrF, and BaF molecules

ESR spectra of MgF, CaF, SrF, and BaF molecules in their ground Σ2 states were measured while trapped in solid neon and argon matrices at 4°K. g tensors and hyperfine structure (hfs) constants for interaction with 19F, and in the case of SrF and BaF, with 87Sr and 137Ba, were determined. In all cases less than 4% of the spin density is on the F atom, supporting the evidence for their extreme ionicity. The variation in the anisotropic character of the 19F hfs probably indicates a slight increase in covalency in the lighter molecules. The hf interaction with the metal nucleus is quite anisotropic, demonstrating that the unpaired s electron on the M+ ion actually has appreciable p and d character, i.e., that the spherical s electron orbit in the free M+ ion is highly distorted by the F− ion in the molecule. This was supported by an approximate variational calculation considering the F− ion as a point charge. A negative Δg⊥ for the MgF molecule indicates that the lowest-lying Π2 state is regular, in support of Walker and Richards' reinterpretation of the λ-type doubling.

Infrared Spectra of the Lithium Halide Monomers and Dimers in Inert Matrices at Low Temperature

The infrared absorption spectra of lithium fluoride, chloride, and bromide vaporization products have been investigated between 2–37 μ in solid argon, krypton, xenon, and nitrogen matrices at liquid-hydrogen and liquid-helium temperatures. Both the natural lithium salts containing 93% 7Li and 6Li salts as well as equimolar isotopic mixtures were studied. The solvent shifts of the monomers were found to confirm the isotopic invariance of the ratio Δω/ω as predicted by Buckingham. Serious deviations from the Kirkwood—Bauer—Magat relation were, however, observed. These shifts have also been discussed in terms of specific solute—solvent interactions. Two dimer vibrational frequencies were definitely characterized by means of isotopic substitutions and these frequencies were assigned. They represent in-plane stretching modes of the planar rhombus, the higher energy vibration being of symmetry b3u (X—X axis polarized) and the lower energy vibration b2u, (Li–Li axis polarized).

Infrared Spectrum and Structure of Gaseous Al2O

The infrared absorption spectrum of Al2O trapped in solid argon and krypton matrices has been observed. It is possible from the observed spectra and isotope shifts for Al216O and Al218O to conclude that the molecular symmetry of Al2O is C2v and that the Al–O–Al angle is probably not far from 145°. Force constants and the bending frequency v2 have been calculated. Reanalysis of the ultraviolet spectra of exploding aluminum wires provides additional support both for the bent structure and for the calculated value of v2. The Al–O bond distance is estimated to be 1.66 Å. The three fundamental frequencies for Al216O in an argon matrix are (in cm—1): v1 = 715, v2 = [238]; v3 = 994.