Showing papers by "Lester Andrews published in 1987"
TL;DR: In this article, the authors studied the FTIR spectra of ammonia from 200 to 5200 cm−1 over a wide range of concentration and temperature conditions in solid neon, argon, and nitrogen matrices.
Abstract: FTIR spectra of ammonia have been studied from 200 to 5200 cm−1 over a wide range of concentration and temperature conditions in solid neon, argon, and nitrogen matrices. Dimer bands appear between monomer and higher aggregate absorptions and exhibit intermediate growth behavior on sample annealing and concentration changes. Comparison of spectra in solid argon at 5 and 12 K shows unrelaxed monomer absorptions at 12 K, which almost completely vanish at 5 K without any difference in the dimer spectrum; this indicates that the NH3 submolecules are relaxed in the matrix‐isolated dimer. One antisymmetric and two symmetric N–H stretching modes were observed for the dimer, which follow the 14NH3–15NH3 and NH3–ND3 shifts of their monomer analogs. The dimer N–H stretching modes are intensified by fivefold relative to the dimer umbrella bending mode as compared to the same relative monomer band intensities, which is diagnostic of the hydrogen bonding interaction. The matrix dimer spectra show that one N–H bond fro...
94 citations
TL;DR: In this article, a red visible photolysis of the PH/sub 3/O/Sub 3/ complex, formed by reagent codeposition with excess argon at 12-18 K, gave seven major products.
Abstract: Red visible photolysis of the PH/sub 3/-O/sub 3/ complex, formed by reagent codeposition with excess argon at 12-18 K, gave seven major products, which are grouped by wavelength-dependent photochemical changes and identified by using /sup 16,18/O/sub 3/ and PH/sub x/D/sub 3-x/ (x = 0, 1, 2, 3) mixed isotopic precursors. The primary products are phosphine oxide (H/sub 3/PO) and phosphinous acid (H/sub 2/POH), structural isomers that were not interconverted by further irradiation, and phosphonic acid ((HO)/sub 2/HPO). The intermediate species HPO, also produced on red photolysis, gave way to HOOPO and HP(O/sub 2/)O on blue-green irradiation. Metaphosphoric acid (HOPO/sub 2/) absorptions increased throughout the irradiation sequence.
72 citations
66 citations
TL;DR: In this paper, the 1377 cm−1 matrix band is assigned to ν3 of linear, centrosymmetric HF−2, based on agreement with solid state and matrix ion pair spectra, and ab initio calculations, and a proper H/D ratio (1.427) for a linear centroid symmetric species.
Abstract: Argon diluted samples of HF were bombarded by low energy electrons (150–400 eV) from a thermionic electron source during condensation at 12 K. Several polyfluoride anions, which have extremely strong hydrogen bonds, were characterized using matrix infrared spectroscopy. Three principal ions were trapped in the argon matrix: HF−2 (1377 cm−1), H2F−3 (1815 cm−1), and ArnH+ (904 cm−1). Electron impact experiments performed with HF/DF mixtures gave counterpart absorptions: DF−2 (965 cm−1), HDF−3 (1707 cm−1), D2F−3 (1391 cm−1), and Arn D+ (644 cm−1). The 1377 cm−1 matrix band is assigned to ν3 of linear, centrosymmetric HF−2, based on agreement with solid state and matrix ion pair spectra, and ab initio calculations, and a proper H/D ratio (1.427) for a linear centrosymmetric species. However, this assignment challenges the recent 1848 cm−1 gas phase assignment to ν3 of HF−2 using laser spectroscopy; the 1848 cm−1 absorption exhibits an H/D ratio (1.323) that is too low for the ν3 vibration of centrosymmetric H...
30 citations
TL;DR: In this article, the intensity ratios of one-to-one complexes between Li, Na, K, and Cs atoms and NH/sub 3/ have been studied by using matrix IR spectroscopy.
Abstract: One-to-one complexes between Li, Na, K, and Cs atoms and NH/sub 3/ have been studied by using matrix IR spectroscopy. New bands at 1133, 1079, 1064, and 1049 cm/sup -1/ are assigned to perturbed nu/sub 2/ modes, and bands at 3277, 3294, 3292, and 3287 cm/sup -1/ are assigned to the perturbed nu/sub 1/ ammonia submolecule modes of the Li--NH/sub 3/, Na--NH/sub 3/, K--NH/sub 3/, and Cs--NH/sub 3/ complexes, respectively. The corresponding bands for K and /sup 15/NH/sub 3/, NH/sub 2/D, NHD/sub 2/, and ND/sub 3/ complexes are also assigned. The intensity ratios of nu/sub 1/ to nu/sub 2/ for the ammonia submolecule modes in the Li, Na, K, and Cs complexes are larger by factors of 15, 20, 30, and 35, respectively, than the corresponding ratio for isolated ammonia. The intensification and position of nu/sub 1/ in the complex and the alkali metal-ammonia interaction are consistent with calculations of a very small ammonia ..-->.. metal charge transfer where the alkali atom acts as a weak Lewis acid for Li and Na. The increased ammonia interaction with K and Cs may suggest a possible acid-base role reversal for the heavier alkali complexes. At higher metal/ammonia concentrations higher aggregate bands ofmore » (M)/sub n/--NH/sub 3/ nature are also observed.« less
30 citations
TL;DR: In this article, the Hartree-Fock SCF calculations were used to study the formation of three different complexes with nitric oxide and nitrogen dioxide in argon matrices and showed that the unpaired electron was contained in a π antibonding orbital which is in the plane of the NO−HF and ONO−HF complexes.
Abstract: HF complexes with nitric oxide and nitrogen dioxide were prepared in argon matrices and studied using IR spectroscopy and unrestricted Hartree–Fock SCF calculations. The results indicate the formation of three different complexes NO‐‐HF, ONNO‐‐HF, and ONO‐‐HF, in which the hydrogen atom of HF is bound to an oxygen atom of the base in each complex. Perturbations in the N–O stretching base submolecule modes were observed in each complex and all were blue shifted with respect to the free base. From the calculations, the unpaired electron was found to be contained in a π antibonding orbital which is in the plane of the NO–HF and ONO–HF complexes.
26 citations
TL;DR: In this article, Hartree-Fock (SCF) calculations were used to construct 1:1 complexes with methane, silane, and germane and showed that the IC inactive symmetric C-H stretch in CH4 was observed in the CH4−−FH complex as a weak band at 2914 cm−1.
Abstract: HF complexes with methane, silane, and germane were prepared in noble gas matrices and studied using infrared spectroscopy and Hartree–Fock (SCF) calculations. The spectra indicate that two types of 1:1 complexes were formed, a normal one in which the hydrogen of HF is interacting with one hydrogen of silane or germane, and a reverse complex in which the fluorine of HF is interacting with one hydrogen atom of methane. The IR inactive symmetric C–H stretch in CH4 was observed in the CH4‐‐FH complex as a weak band at 2914 cm−1. In the silane‐‐HF and germane‐‐HF complexes, the Si–H and Ge–H stretches were perturbed approximately 50 cm−1 to higher energy relative to the antisymmetric stretch ν3 in each parent molecule, but the ν1 modes were masked by the strong ν3 parent bands. Higher order 1:2 (AH4:HF) complexes were also observed and support the normal or reverse‐type geometry of the 1:1 complexes.
25 citations
TL;DR: Very weak, hydrogen bonded complexes of molecular hydrogen and oxygen with HF have been prepared by condensing the neon diluted reagents at 4-5 K as discussed by the authors. But argon is not an effectively inert medium for very weak complexes where interaction with the solid argon environment is competitive with the H2−HF and O2-HF interactions.
Abstract: Very weak, hydrogen bonded complexes of molecular hydrogen and oxygen with HF have been prepared by condensing the neon diluted reagents at 4–5 K. Infrared spectra of the H2‐‐HF complex revealed a νs(HF) mode at 3938 cm−1 and νc(H2) mode at 4155 cm−1 which are red shifted from isolated molecule values in agreement with theoretical predictions. Increasing the HF concentration produced a 1:2 complex, H2–(HF)2. Similar experimental results were obtained for molecular oxygen complexes using HF and DF; the oxygen fundamental in this complex, however, exhibited a 6 cm−1 blue shift. Spectra of these complexes in argon matrices showed that argon is not an effectively inert medium for very weak complexes where interaction with the solid argon environment is competitive with the H2–HF and O2–HF interactions.
22 citations
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17 citations
TL;DR: In this article, the authors used matrix IR spectroscopy to study one-to-one complexes between Na, K and Cs atoms and H2O and found that perturbed water submolecule vibrations were observed in the bending and stretching regions for each complex.
TL;DR: In this article, hydrogen-bonded complexes between phenylacetylene, phenylpropyne and HF have been prepared by reagent condensation in an argon or nitrogen matrix at 12 K.
TL;DR: In this paper, parent radical cations of octatetraene and decapentaene have been prepared and trapped in solid argon using matrix photoionization methods with both cyclic and acyclic precursors.
Abstract: Parent radical cations of octatetraene and decapentaene have been prepared and trapped in solid argon using matrix photoionization methods with both cyclic and acyclic precursors. Visible absorption spectra are assigned to the all-trans cation isomer and several structures with increasing numbers of cis configurations. Irradiation into these bands with argon and krypton ion laser lines caused reversible rearrangements among several of the configurations for octatetraene and decapentaene cations. The cold matrix provides an excellent medium for studying molecular cation rearrangements where one structure can absorb light and other structures formed can be relaxed by the matrix before dissociation