William Weltner

Spectroscopy of Carbon Vapor Condensed in Rare‐Gas Matrices at 4°K. III

For C3, controlled warming of neon matrices containing carbon vapor caused the multiple sites for C3 molecules to disappear. The assignments of vibronic transitions in the 1IIu←X1Σg+ system could then be made more definite using the parameters of Gausset, Herzberg, Lagerqvist, and Rosen. Two unaccounted‐for bands were attributed to transitions involving v3′≅840 cm−1. This low value was rationalized by comparison with other similar molecules. The 1Σu+←X1Σg+ transition of C3 in a neon matrix was not observed in the ultraviolet out to 1950 A.For C2, the spectrum of carbon—neon matrices, before and after warming to 12°K, indicated that the absorption bands in the region of 4000–6000 A are probably not the C2 Swan system but may be due to a larger carbon molecule. A band at 2320 A in neon was attributed to the (0, 0) band of the Mulliken system (1Σu+←x1Σg+ of C2. These and other observations indicate that the trapping of C2 in the excited 3IIu state in matrices is doubtful.CNN is formed in neon matrices contai...

ESR of Cu(NO3)2 and CuF2 Molecules Oriented in Neon and Argon Matrices at 4°K

An experimental apparatus is described which allows the trapping of preferentially oriented molecules in neon and argon matrices at 4°K and the measurement of their ESR spectra at various orientations relative to the magnetic field. Application to Cu(NO3)2, vaporizing at 150°C, and CuF2, vaporizing at 925°C, demonstrates that the degree of orientation is dependent upon the temperature of the vaporizing molecule and the matrix gas used. The ESR spectra of highly oriented Cu(NO3)2 in neon at 4°K (there was essentially no orientation in argon) indicate that the molecule is planar with the four nitrate oxygen atoms surrounding the Cu++ ion in a square array. The g and A values are very similar to those found in copper chelate molecules: g∥ = 2.2489±0.003, g⊥ = 2.0522±0.0005, A∥ (63Cu) = 570±3 Mc/sec, and A⊥ (63Cu) = 50±3 Mc/sec. Computer simulation of the spectra not only confirms this assignment but provides an estimate of the degree of orientation as a function of the inclination. CuF2 isolated in argon at ...

Spectroscopy of Carbon Vapor Condensed in Rare‐Gas Matrices at 4° and 20°K. I

The molecules vaporizing from graphite at 2300° to 2600°K have been trapped in neon, argon, and xenon matrices at 4° and 20°K. The near‐ultraviolet bands of C3, beginning at 4050 A in the gas, have been observed in the absorption spectra of these matrices but shifted to 4057 A in neon, 4102 A in argon, and 4226 A in xenon. The neon spectrum is strikingly similar to low‐temperature gaseous spectra, including cometary spectra, but the matrix bands occur in groups about 100 cm—1 wide. The infrared spectrum yields a strong band at 2038 cm—1 in argon (2042 cm—1 in neon) which is assigned to v3″, the asymmetric stretching frequency of C3 in the ground electronic state. When the argon matrix is allowed to warm up, diffusion occurs, and larger carbon molecules, C4, C5, C6, etc., are formed, causing the appearance of many new bands in the infrared. The Swan bands of C2 are observed in neon and argon matrices, but only after some annealing of the matrix has occurred by warming. The vibrational frequency of C2 in th...

Spectroscopy of Silicon Carbide and Silicon Vapors Trapped in Neon and Argon Matrices at 4° and 20°K

The numerous molecules vaporizing from silicon carbide at 2600°K and from silicon at 2300°K have been trapped in neon and argon matrices at 4° and 20°K and studied spectroscopically in the infrared, visible, and near‐ultraviolet regions. The Si2 and SiC2 molecules have been observed, and less definitely, also Si2C, Si2C3, Si3, and Si4. In the case of silicon carbide vaporization, the absorption spectrum of SiC2 appears strongly at 4963 A in neon and 4993 A in argon as compared with 4977 A in the gas. The spectrum agrees with the gaseous observations of McKellar and Kleman, but with the addition of three weak but distinct bands. It is interpreted as a 1Πu←X1Σ+ transition where the vibrational assignments in these states are now as follows: 1Σ+, ν1″=853, ν2″=300, ν3″=1742 cm—1; 1Π, ν1′=1015, ν2′=230, ν3′=1461 cm—1. The vibrational structure in the upper state is anomalous in that it requires a large positive value for x13′. The spectrum of symmetrical Si2C is believed to occur at 5300 A in argon with ν1′=50...

Matrix Isolation of High‐Temperature Vapors: Boric Oxide

Abstract : The matrix isolation technique was extended to allow molecules which are in equilibrium with solids at high temperatures to be trapped and studied at low temperatures. A beam of the hot vapor issuing from a Knudsen cell or a heated surface is premixed with a large excess of argon or xenon just prior to condensation at 20 K. The method was applied to boric oxide vapor which was vaporized from the liquid at 1400 K. The infrared absorption spectrum of the B2O3 molecule in a solid inert gas matrix was measured between 1/280 cm and 1/3600 cm and compared with the known vapor emission spectrum. Several new bands were found near 1/500 cm which led to a considerable alteration in the vibrational assignment and the thermodynamic properties of the gaseous molecule. The infrared spectrum of B2O2 (produced by heating boron plus boric oxide) isolated in a matrix yielded one absorption band which agreed with the emission spectrum. A general program (IBM 7090) was used for the calculation of molecular force constants from assigned fundamental vibrational frequencies. (Author)

ESR and Optical Spectroscopy of ScO, YO, and LaO in Neon and Argon Matrices; Establishment of Their Ground Electronic States

ScO, YO, and LaO were vaporized from the solid oxides at temperatures near 2500°K and trapped in neon and argon matrices at 4° and 20°K. ESR spectra of these matrices show that the ground states of all of the molecules are 2Σ. The measured magnetic parameters for the three molecules are as follows: ScO, g=2.00±0.01, A=2.01±0.01 kMc/sec; YO, g=2.003±0.002, A=0.803±0.003 kMc/sec; LaO, g=2.01±0.01, A=3.89±0.01 kMc/sec. The A values then yield nuclear hyperfine‐structure separations (Δν) of 0.27, 0.03, and 0.52 cm−1, respectively, and explain the large splittings observed in the optical spectra of ScO and LaO.The optical spectra of the matrices exhibit the two transitions A2Π←X2Σ and B2Σ←X2Σ observed in the gas spectra of these molecules. The bands are exceptionally broad and shifted in the matrix relative to the gas, much more so than in the matrix spectra of other transition‐metal diatomic oxides. Illumination of the matrices with tungsten light leads to a gradual disappearance of the absorption bands and l...

Spectroscopy of TaO and TaO2 in Neon and Argon Matrices at 4° and 20°K

The TaO and TaO2 molecules vaporizing from tantalum oxide at 2270°K have been trapped in neon and argon matrices at 4° and 20°K and studied spectroscopically in the infrared, visible, and near‐ultraviolet regions. TaO spectra exhibit the three electronic transitions observed in the gas and analyzed by Premaswarup and Barrow. The matrix spectra lead to a probable revision of the 4155 A gas transition, indicating that TaO has a 2Δr ground state. In all, 16 electronic transitions from the X 2Δ32 level have been distinguished by 18O substitution and most of the upper‐state vibrational frequencies determined. Two electronic transitions of TaO2 in a neon matrix occur at 8607 A (strong) and 6159 A (weak). The bending frequency in the upper state dominates both of the band systems and indicates that the O–Ta–O angle undergoes a large change in the transitions. The infrared spectrum of TaO2 exhibits two bands, suggesting that the molecule is bent in the ground state. Vibrational frequencies in the ground state are...

Spectroscopy of tungsten oxide molecules in neon and argon matrices at 4° and 20°K

WO, WO2, and also WO3, W2O6, W3O8, W3O9, W4O12 have been trapped in neon and argon matrices at 4° and 20°K and studied spectroscopically in the infrared, visible, and near-ultraviolet regions. The molecules were prepared by vaporization from the solid oxides at 1600°K or by passing 16O2 or 18O2 over tungsten at 1900 to 2950°K. Seven electronic transitions, lying between 3500 and 6000 A, are observed in the absorption spectrum of WO. These progressions are generally found to be strongly perturbed in the W16O spectra, but regular in W18O. The strong system of bands with (0, 0) at 4807 A in neon, observed in gas emission at 4806.4 A, is essentially unperturbed in both molecules. The vibrational frequencies in the excited electronic states are determined and the various perturbations of the levels in W16O discussed. The spectrum of WO2 is similar to that of bent TaO2 and exhibits two electronic transitions in a neon matrix at 7890 A (strong) and 7806 A (weak). A long progression of the bending frequency in the upper state appears in both systems indicating that the OWO angle undergoes a large change in the transitions. From the 7890-A system, it is found that ν1′ = 972, ν2′ = 300 cm−1, ν3′ = ?; the infrared spectrum yields ν1″ = 992, ν2″ = ?, ν3″ = 928 cm−1. The MO schemes of TaO and TaO2 are used to predict 3Σ− and 3A1 ground states for WO and WO2, and on this basis the excited states and assignment of electronic transitions are considered. A system of absorption bands beginning at 3452 A in neon is tentatively assigned to WO3. The larger molecules, WO3, W2O6, etc., produce many bands in the infrared some of which can be assigned to particular oxide molecules by varying the conditions of vaporization.