Arnold M. Bass

Slit Function Effects in the Direct Measurement of Absorption Line Half-Widths and Intensities*†

The distortion of spectral lines by the finite band pass of spectrometers is an effect which must be considered in measuring line shape parameters. The differences between actual line half-widths and line intensities and those which would be obtained directly from measurements by spectrometers with Gauss and Cauchy shaped slit functions have been calculated for Lorentz and Doppler lines of varying widths and intensities. A method of utilizing these results to correct actual measurements is developed.

Matrix-isolation study of the reaction of f atoms with co - infrared and ultraviolet spectra of the free radical fco.

FCO has been obtained in a CO and in an Ar matrix at 4°, 14°, and 20°K by the reaction with CO of F atoms produced upon photolysis of OF2, of NF2, or of t‐N2F2, as well as by the photolysis of F2CO or of HFCO. The three vibrational fundamentals of the free radical FCO appear at 1855, 1018, and 626 cm−1. Experiments employing 13C16O and 12C18O confirm the infrared identification of FCO. In ultraviolet‐absorption studies on matrix‐isolated FCO an extensive series of bands has been observed between 2200 and 3400 A. The most prominent progression in this system involves bands spaced at approximately 650‐cm−1 intervals. It is likely that this progression is associated with the upper‐state bending mode of FCO. F2CO and (FCO)2 are also produced in the reaction of F atoms with a CO matrix, and features of their infrared spectra are reported. A supplementary observation of the ultraviolet‐absorption spectrum of gaseous F2CO shows a band system between 1800 and 2100 A, with spacings of approximately 1700 cm−1. Presumably this system is contributed by the n→π* carbonyl transition. The approximate geometric structure and the nature of the chemical bonds of FCO are discussed, and the mechanisms of formation of this species and of the other observed products are considered. An estimate of the thermodynamic properties of FCO is given.

Matrix Isolation Study of the Photolysis of Cyanogen Azide. The Infrared and Ultraviolet Spectra of the Free Radical NCN

The infrared and ultraviolet absorption spectra of the free radical NCN have been observed following photolysis at wavelengths longer than 2800 A of cyanogen azide isolated in argon, nitrogen, carbon monoxide, and carbon dioxide matrices. The infrared‐active vibrational fundamentals of NCN appear at 423 and at 1475 cm−1. Isotopic studies are consistent with this identification. The force constants and thermodynamic properties of NCN have been estimated. Two ultraviolet absorption systems are associated with NCN. The first of these, previously reported, lies near 3290 A. The second system is comprised of a progression of bands spaced at intervals of approximately 1045 cm−1, lying between 3000 and 2400 A. The nature of this second transition is discussed. At wavelengths longer than 2800 A both cyanogen azide and NCN have been found to photolyze with the production of carbon atoms. The nature of the new features observed in the infrared and ultraviolet spectral regions after photolysis with short‐wavelength radiation is considered.

Flash Photolysis of Methane in the Vacuum Ultraviolet. II. Absolute Rate Constants for Reactions of CH with Methane, Hydrogen, and Nitrogen

By means of kinetic spectroscopy, the concentration of CH has been measured in the flash photolysis of methane. Measurements were made by following the attenuation of C 2Σ+←X 2Π Q branch at 3143 A, where the disappearance of CH is of the first order in CH. Experiments were conducted with pure methane, methane+H2, and methane+N2. The reactions and the corresponding rate constants in mole−1 cm3 sec−1 are CH+CH4→C2H4+H,k=1.5×1012;CH2+H2→CH3,k=6.2×1011;CH+N2→products,k≃4.3×1010;CH+CH→C2H2,k≃1.2×1014.

Flash photolysis of carbon suboxide: absolute rate constants for reactions of C(3P) and C(1D) with H2, N2, CO, NO, O2 and CH4

The vacuum ultraviolet flash photolysis of C3O2 in the 159.0 nm absorption band has been investigated. The major primary products are C(1S), C(1D), C(3P), and CO. The species C2 and C3 have also been observed but are of minor importance in the overall reaction scheme. A number of pressure independent reactions involving C(3P), C(1D), and C(1S) with CO, CH4, N2, NO, O2, and H2 have been observed by means of the kinetic-spectroscopic method. The rate constants measured at room temperature are summarized here (cm3 s-1 molecule-1): C(3P) + CH4 → C2H4 (?) k < 5 x 10-15 (7) C(1D) + CH4 → C2H2 + H2 k = 3.2 x 10-11 (8) C(1D) + N2 → C(3P) + N2 k ≈ 2.5 x 10-12 (10) C(3P) + NO → CN + O k = 1.1 x 10-10 (12) C(1D) + NO → CN + O k = 9.2 x 10-11(13) C(1D) + H2 → CH + H k = 4.15 x 10-11 (18) C(1S) + H2 → CH + H(?) k < 5 x 10-12 (19) C(3P ) + O2 → CO + O k = 3.3 x 10-11 (20) C(1D) + O2 → CO + O(?) k < 5 x 10-12 (22) The pressure dependent reaction rates of C(3P) with N2, CO, and H2 have been qualitatively measured and are discussed in detail.

Electronic spectra and structure of the hydrogen halides the b 3Πi and C 1Π states of HI and DI

Abstract The absorption spectra of HI and DI below 1900 A have been photographed at high resolution. Analyses of the “B” ← X and C ← X transitions show that the “B” state is the 3Πi component of a 3Πi state (designated here as b) and the C state is a 1Π state. Both b 3 Π i and C 1 Π originate from the same π3σ configuration, exhibit strong predissociations, and show some small Case c effects. The transition from approximately Λ, S toward Ω , ω coupling is discussed for the b and C states of the hydrogen halides, HCl, DCl, HBr, DBr, HI, and DI. Effective molecular constants are presented for the b and C states of HI and DI.

Absorption and Laser‐Excited Fluorescence of Matrix‐Isolated CuO

Absorption and laser‐excited fluorescence spectra of CuO trapped in variousmatrices have been observed. The matrix data and previously observed gas‐phase data are consistent withν00 (martix)ν00 (gas)5ν (martix)(cm−1)(cm−1)(cm−1)(cm−1)C23 550B(2Σ?)20 49020 953624A(2Π?)3 9004 460605(2Π1/2 − 2Π3/2 = 275)X(2Π)00665(2Π1/2 − 2Π3/2 ≃ 200)for the lowest states of CuO. It is shown that the matrix‐isolation technique can beused to “tune” an absorption into coincidence with a laser line in order to observefluorescence. The vibrational relaxation of CuO in a solid matrix requires on the order of 105 vibrations.

Matrix‐Isolation Spectra of Discharge “Sputtered” Metals

Atomic Cu, Ag, Cd, and Fe are produced by bombarding the appropriate metal with positive ions from a microwave discharge. The process is similar to sputtering. The metal atoms are trapped in an inert‐gas matrix on a cold window and their uv spectra observed. This is a new method for isolating high‐melting materials in a matrix for spectroscopic study.

Experimental test of a two-layer model characterizing emission-line profiles

Deuterium Lyman-α line profiles, generated from a microwave-powered lamp containing flowing mixtures of deuterium in helium, were examined spectroscopically under high resolution. The primary purpose was to test a simple two-layer model describing the line shape emerging from a discharge zone containing both emitting and absorbing atoms. This simple model characterized the experimentally obtained line shapes under varying conditions of atom densities and line self-reversal. The kinetic (translational) temperature of the discharge could be calculated from the data. Resonance interaction between ground-state D(2S) atoms and excited D(2P) atoms is offered as an explanation for the experimentally observed line asymmetries. The presence of line self-reversal significantly amplifies the small spectral shifts between the absorption and emission lines. These shifts can be calculated from the model.

Large-Aperture Grating Spectrograph Utilizing Commercial Camera Components*†

A compact, large-aperture spectrograph utilizing commercially available optical components has been designed and constructed. Light is admitted through an adjustable bilateral slit and is collimated by a 300-mm f/4.5 telephoto camera lens. The dispersive element is a 102 × 102 mm, 600-lines per mm plane reflection grating with a first-order blaze at 1.0 μ. The spectrum is photographed with a single-lens reflex 35-mm camera equipped with a 75-mm f/1.5 lens. One frame covers a spectral range of approximately 8000 A with a dispersion of about 200 A/mm in the first order.