Showing papers by "Lester Andrews published in 1988"

Matrix reactions of methylsilanes and oxygen atoms

Abstract: The reaction of oxygen atoms and substituted methylsilanes have been investigated in argon matrices at 14-17 K. Products were identified by using isotopic /sup 18/O/sub 3/ precursor and deuterium substitution in the Si-H bonds. With MeSiH/sub 3/, Me/sub 2/SiH/sub 2/, and Si/sub 2/H/sub 6/, the silanols MeSiH/sub 2/OH, Me/sub 2/SiHOH, and SiH/sub 3/SiH/sub 2/OH were formed, respectively. These molecules contain the Si-O-H functional group with 3708-3711-cm/sup -1/ O-H stretching frequencies. For Me/sub 4/Si, the carbinol Me/sub 3/SiCH/sub 2/OH was produced with a lower 3637-cm/sup -1/ O-H stretching frequency. Me/sub 3/SiH was different: the silanol was not observed, but instead a product tentatively identified as CH/sub 2/=Si(OH)Me was formed. Also, the silanones H/sub 2/SiO and Me(H)SiO were produced from MeSIH/sub 2/, Me(H)SiO and Me/sub 2/SiH/sub 2/ were formed with Me/sub 2/SiH/sub 2/, and Me/sub 2/SiO was again observed with Me/sub 2/SiH. These silanones contain the Si=O functional group with stretching frequencies of 1201-1209 cm/sup -1/.

Matrix trapping of two structural arrangements of weak complexes

Abstract: FTIR spectra of Ar/CO/HF mixtures rapidly frozen at 12 and 5 K contained a weak new absorption at 3907 cm/sup -1/ in addition to the strong OC--HF complex band at 3789 cm/sup -1/. The DF counterpart absorbance at 2866 cm/sup -1/ was a larger fraction of the absorbance for OC--DF at 2781 cm/sup -1/. The former new bands were generally favored by slower spray-on rates and were destroyed on annealing that increased the latter bands. These weaker new bands are assigned to the reverse complexes CO--HF and CO--DF that calculations predict to be less stable than the carbon-bonded structures observed in the gas phase and in larger yield in matrices. An analogous situation was found for Ar/HCN/HF mixtures which revealed both HF--HCN and HCN--HF. Apparently matrix formation relaxes these molecules fast enough to trap the less stable complex structures that are not observed in supersonic nozzle expansion experiments.

Matrix isolation study of electron impact on H2O. Infrared spectrum of OH− in solid argon

Abstract: A thermionic electron source capable of delivering 10–200 mA of electrons at low energies (30–200 eV) has been mated to a matrix isolation apparatus and employed to study electron impact on water. Three products were trapped in the argon matrix; OH radical (3452.7, 3478.1 cm−1), ArnH+ (903.7 cm−1), and a new species absorbing at 3548.9 cm−1 with a 3554.0 cm−1 shoulder. The latter is identified as OH− owing to diatomic D and 18O isotopic shifts and agreement with recent gas phase work. The 3548.9 cm−1 absorption is assigned to the R(0) vibration–rotation band of OH−, which is red shifted 42.6 cm−1 by the argon matrix. This shift is slightly more than the 38.4 cm−1 matrix shift for the R(0) line of HF. Product band intensities showed no dependence on electron energy above 30 eV but showed a nonlinear dependence on electron current, which suggests that OH is produced by primary electron impact on water and that OH− and ArH+ solvated by argon are produced by secondary processes.

Infrared spectra of the ozone...hydrogen fluoride and sulfur dioxide...hydrogen fluoride complexes in solid argon

Abstract: Argon matrix spectra of the O/sub 3/- -HF and SO/sub 2/- -HF complexes are similar, and the structure deduced for O/sub 3/- -HF from the infrared spectrum is similar to the microwave structure for SO/sub 2/- -HF. All three ozone submolecule fundamentals were observed for the complex, and v/sub 1//sup c/ was considerably enhanced in intensity relative to v/sub 3//sub c/. The asymmetric mixed isotopic ozone complexes exhibited split v/sub 1//sup c/ bands which indicate inequivalent terminal oxygen atoms and attachment of HF at this position in the complex.

Infrared spectra of ClF, Cl2, and Cl complexes with HCl in solid argon

Abstract: Argon mixtures of ClF, Cl2, and Cl atoms have been codeposited with Ar/HCl at 5 and 12 K. Infrared spectra in the HCl stretching region give evidence for the FCl‐‐HCl, Cl2‐‐HCl, and Cl‐‐HCl hydrogen‐bonded complexes. The molecular complexes are more stable in the hydrogen‐bonded than antihydrogren‐bonded forms as no evidence for the latter were observed. The Cl‐‐HCl radical hydrogen‐bonded complex is considerably different from the centrosymmetric (Cl–H–Cl)− anion.

Infrared spectra of hydrazine and products of its reactions with HF, F2, and O3 in solid argon

Abstract: Hydrazine, N/sub 2/H/sub 4/, and its reactions with HF, F/sub 2/, and O/sub 3/ have been studied in an argon matrix. Vibrational assignments have been made for hydrazine, including clarification of the /nu//sub 6/, /nu//sub 10/, and 2/nu//sub 7/ bands. Complexation of N/sub 2/H/sub 4/ with HF produced a strong band at 2928 cm/sup /minus/1/ (/nu//sub s/(HF)) and sharp bands at 940 and 922 cm/sup /minus/1/ (/nu//sub 1/(HF)), as well as several perturbed N/sub 2/H/sub 4/ submolecule absorptions; the frequencies of these bands suggest a chelated structure similar to that for the NH/sub 2/OH-HF complex. Hydrazine and fluorine reacted during deposition to give the NH/sub 2/NHF-HF complex (/nu//sub s/ = 3113 cm/sup /minus/1/, /nu//sub 1/ = 726, 680 cm/sup /minus/1/). Reaction of hydrazine and ozone produced hydroxyhydrazine, NH/sub 2/NHOH, and minor products during deposition; photolysis increased the yield of hydroxyhydrazine. Evidence for an intramolecular hydrogen bond was found for NH/sub 2/NHOH. This matrix study presents the first spectroscopic evidence for both NH/sub 2/NHF and NH/sub 2/NHOH. 32 references, 3 figures, 4 tables.

Infrared spectra of fluoroimide, nitrogen trifluoride, phosphorus trifluoride, and phosphorus trichloride and complexes with hydrogen fluoride in solid argon

Abstract: Infrared spectra of HNF/sub 2/, NF/sub 3/, PF/sub 3/, and PCl/sub 3/ and their complexes with HF were observed in solid argon matrices. An asymmetric structure was deduced for (HNF/sub 2/)/sub 2/ based on comparison with HNF/sub 2/ spectra. Complexation of these bases with HF produced the following bands: HNF/sub 2/, 3681 cm/sup -1/ (nu/sub s/) and 516 and 498 cm/sup -1/ (nu/sub l/); NF/sub 3/, 3913 cm/sup -1/ (nu/sub s/) and 246 cm/sup -1/ (nu/sub l/); PF/sub 3/, 3890 cm/sup -1/ (nu/sub s/) and 258 cm/sup -1/ (nu/sub l/); PCl/sub 3/, 3868 cm/sup -1/ (nu/sub s/). The spectra suggested the formation of a hydrogen bond between HF and the N or P lone pair for all four complexes. A direct correlation between proton affinity and nu/sub s/ was found for fluoro-substituted amines, allowing prediction of the HNF/sub 2/ proton affinity as 163 +- 5 kcalmol and that of NH/sub 2/F as 181 +- 5 kcalmol. Basicity trends in nitrogen and phosphorus compounds are discussed.

Optical spectra of Yb atoms and dimers in rare gas matrices

Abstract: Matrix isolated Yb vapor spectra show absorptions due to atoms, dimers, and higher aggregates. The atomic spectrum reveals strong 395 and 344 nm bands and very sharp weaker 267 and 255 nm absorptions in solid argon. The spectrum of Yb2 shows extensive vibrational stucture around 550 nm both in Ar and Kr matrices with a spacing of 48 cm−1. This absorption is assigned to a 6s2(1S0)6s2(1S0)(1Σ+g) →6s2(1S0)6s6p(1P1)(1Σ+u) transition similar to the one observed for group IIA metal dimers. Higher aggregate spectra overlap with the 550 nm dimer and weak atomic band.

Matrix infrared study of NH−2 produced by electron impact on NH3

Abstract: Electron impact of dilute Ar/NH3 samples during condensation at 12 K produced six new infrared bands: 3552, 3217, 3152, 3133, 1523, and 1496 cm−1. The 3552 cm−1 band has been assigned to OH−, the 3133 cm−1 band to NH, and the 3217 and 1496 cm−1 bands to NH2 radical by earlier workers. The 3152 and 1523 cm−1 bands exhibit proper 15N shifts to be assigned to the NH−2 anion isolated in solid argon.

Photochemical reactions of ClF and BrF with hydrogen in solid argon. Infrared spectra of mixed hydracid dimers

Abstract: Argon diluted samples of H2 and ClF were codeposited at 10 K, and no reaction was observed. Photolysis produced a sharp 2834.5, 2832.5 cm−1 doublet, in agreement with (HF)(HCl) dimer from HF and HCl codeposition experiments. Irradiation at 14–16 K markedly increased the mixed dimer and produced weak monomer and dimer bands of HCl and HF, mixed trimer absorptions, and a sharp band at 3857.9 cm−1 for the Cl‐‐HF radical complex. In similar experiments with HD, two mixed dimers, (HF)(DCl) and (HCl)(DF), were formed; likewise, photolyzing D2 with ClF produced two mixed dimers of the form (DF)(DCl) and (DCl)(DF). In the H2 and BrF system, photolysis produced a sharp absorption at 3814.6 cm−1, in agreement with (HBr)(HF) dimer from HBr and HF codeposition experiments, and a new 3830.5 cm−1 band due to the Br‐‐HF radical complex. In a parallel study with HD, two mixed dimers, (HBr)(DF) and (DBr)(HF), were observed while only one mixed dimer, (DBr)(DF), was formed by BrF and D2. In complementary experiments with H...

Infrared Spectra of Hydrazine and Products of Its Reactions with HF, F2, and O3 in Solid Argon.

Abstract: Hydrazine, N/sub 2/H/sub 4/, and its reactions with HF, F/sub 2/, and O/sub 3/ have been studied in an argon matrix. Vibrational assignments have been made for hydrazine, including clarification of the /nu//sub 6/, /nu//sub 10/, and 2/nu//sub 7/ bands. Complexation of N/sub 2/H/sub 4/ with HF produced a strong band at 2928 cm/sup /minus/1/ (/nu//sub s/(HF)) and sharp bands at 940 and 922 cm/sup /minus/1/ (/nu//sub 1/(HF)), as well as several perturbed N/sub 2/H/sub 4/ submolecule absorptions; the frequencies of these bands suggest a chelated structure similar to that for the NH/sub 2/OH-HF complex. Hydrazine and fluorine reacted during deposition to give the NH/sub 2/NHF-HF complex (/nu//sub s/ = 3113 cm/sup /minus/1/, /nu//sub 1/ = 726, 680 cm/sup /minus/1/). Reaction of hydrazine and ozone produced hydroxyhydrazine, NH/sub 2/NHOH, and minor products during deposition; photolysis increased the yield of hydroxyhydrazine. Evidence for an intramolecular hydrogen bond was found for NH/sub 2/NHOH. This matrix study presents the first spectroscopic evidence for both NH/sub 2/NHF and NH/sub 2/NHOH. 32 references, 3 figures, 4 tables.