Don M. Yost

The molecular structure of isocyanic acid from microwave and infra-red absorption spectra

Experimental investigations of the infra-red and microwave spectra of the slightly asymmetric rotor, HNCO, have been made, and the structure of the molecule has been determined.

The Raman Spectra and Molecular Constants of the Hexafluorides of Sulfur, Selenium and Tellurium

The Raman spectra of the gaseous and liquid hexafluorides of sulfur, selenium and tellurium were determined (Table I). Three lines for each substance were observed and this is the number permitted by the selection rules for a regular octahedral molecule. Frequency formulae based on central forces were derived, and these, together with the appearance of the spectra, were used to assign the observed frequencies to the proper modes of vibration. Estimates of the magnitudes of the forbidden frequencies were made. A provisional value of —238,000 cal. is given for the free energy of formation of SF6 (g) at 25°.

Kinetics of the Rapid Gas Phase Reaction between NO, NO2, and H2O

Using the absorption of light by nitrogen dioxide as a measure of its concentration, the rate of the gas phase reaction NO+NO_2+H_2O=2HNO_2 was measured over a fivefold range of water vapor and nitrogen dioxide concentrations, with nitric oxide greatly in excess. Changes in light intensity were detected by means of an electron‐multiplier photo‐tube and recorded by photographing the screen of a cathode‐ray oscilloscope. Half‐times as short as 0.014 sec were observed. The reaction rate was found to depend more strongly upon the concentration of water vapor than upon that of nitrogen dioxide and to be kinetically consistent with a mechanism involving termolecular collisions. The equilibrium constant of the reaction has been calculated and its order of magnitude experimentally confirmed, and a lower limit has been fixed for the rate of dissociation of nitrogen sesquioxide.

The Structure of Trifluoromethyl Acetylene from the Microwave Spectrum and Electron Diffraction Pattern

Measurements, in the microwave region, of the J = 3→4 rotational transitions of trifluoromethyl acetylene and several of its isotopic modifications have been made, and the moments of inertia, I_B (in a.m.u.‐A 2), have been found for the ground vibrational state: for CF_3CCH, 175.61_3, CF_3C^(13)CH, 177.02_4, CF_3CC^(13)H, 181.30_2, and for CF_3CCD, 187.46_2. Three lines corresponding to J = 3→4 transitions of CF_3CCH in the excited vibrational state v_(10) = 1, and two lines corresponding to v_(10) = 2 and v_(10) = 3, have also been measured and interpreted according to Nielsons theory of l‐type doubling in symmetric tops. From Stark effect measurements at different electric field strengths the dipole moment of CF_3CCH in the ground vibrational state has been found to be 2.36±0.04 Debye units. For the ground vibrational state the microwave data lead to the following bond distances: C–H, 1.056±0.005A; C≡C, 1.201±0.002A. The C–C and C–F distances were calculated from the measured moments of inertia for several assumed values of the FCF angle. Electron diffraction experiments were also made, and the intensity curves calculated for the assumed microwave models were compared with the observed visual curve. From the combination of microwave and electron diffraction results the best agreement was obtained with the following set of parameters: ∠FCF, 107.5°±1°; C–C, 1.464±0.02A; C–F, 1.335±0.01A.

The Raman Spectra of Boron Trifluoride, Trichloride, and Tribromide. The Effect of the Boron Isotopes

The Raman frequencies v1{1}, 2v2{2}, v3{2}, and v4{2} for BF3(g), BCl3(l), and BBr3(l) were found to be 886 and 783, 1394, 1038 and 1105, 440; 471, 924, 958 and 996, 243; 279, 743, 806 and 846, and 151 cm—1, respectively. The assignment of frequencies was determined by polarization experiments on BCl3 and is confirmed for the three compounds by the results of a normal coordinate treatment. The doubling of v1 in BF3 is ascribed to vibrational resonance between v1 and 2v4. The doubling of v3 in all three compounds is shown to be due to the presence of the two isotopes of boron B10 and B11. A satisfactory assignment of the infrared frequencies of BCl3 is made.

The Raman Spectra and Molecular Constants of Phosphorus Trifluoride and Phosphine

The Raman frequencies of PF3(l) were found to be ω1(1), 890 cm‐1; ω2(1), 531 cm‐1; ω3(2), 840 cm‐1; and ω4(2), 486 cm‐1, indicating a regular pyramid structure of the molecule. Three frequencies were observed for PH3(l): 2306 cm‐1, 1115 cm‐1 and 979 cm‐1. With the aid of electron diffraction data the standard virtual entropies of PF3(g), PCl3(g), AsF3(g), and AsCl3(g) at 25°C are calculated to be 64.2, 74.7, 69.2, and 78.2 cal./deg., respectively; that of PH3(g) is estimated to be 50.5 cal./deg. These data lead to the following free energies of formation at 25°C: AsCl3(g), ‐62,075 cal.; PH3(g), 2750 cal.; PCl3(g), ‐62,220 cal.

The Analysis of the Raman Spectra of Si2Cl6(l) and of Si2H6(g)

The Raman spectra of Si2H6(g) and of Si2Cl6(l) have been photographed. Polarization measurements of the stronger lines of Si2Cl6 have been made. From a consideration of the relations among the modes of vibration of similar molecules having different symmetry, the analysis of the observed lines is facilitated by a knowledge of the assignments of the fundamental frequencies of SiH4, HSiCl3 and BrSiCl3. A definite assignment is made for the three observed lines of Si2H6. A tentative assignment of the observed lines of Si2Cl6 is made and some evidence is presented for the existence of internal rotation in this molecule at room temperature.

Photo-Chemical Reduction of Water by Europium (II) Ion, and the Magnetic Susceptibilities of Europium (II) and (III) Ions

The slow reaction of europium (II) ion with hydrogen ion or water to produce hydrogen and europium (III) ion has been previously reported. Prior to an investigation of the aqueous chemistry of europium (II) ion, the study of this reaction was undertaken. It was decided to follow the course of the reaction by observing the change in magnetic susceptibility of the reaction mixture, using a Gouy balance. This method was suggested by the aforementioned work of R. A. Cooley. Preliminary experiments showed that solutions 0.25 min europium (II) chloride and about 0.3 m in hydrochloric acid were stable over periods of weeks when kept in the dark, but evolved hydrogen and changed susceptibility rapidly when exposed to bright light (either sunlight or a tungsten lamp). One other such system has been reported in the literature. Poterill, Walker, and Weiss investigated the photo-chemical reduction of water by iron (II) ion.

The Raman Spectra of Carbon and Silicon Tetrafluorides

We have photographed the Raman spectra for the tetrafluorides of carbon and silicon in both the liquid and gaseous states. The results are presented in Table I together with the Raman frequencies for CCl4 for purposes of comparison.

Dipole Moment and Electric Quadrupole Effects in HNCO and HNCS

Interaction of the electric quadrupole moment of the nitrogen nucleus with the molecular electric fields of isocyanic and isothiocyanic acids results in a hyperfine splitting of the rotational trnasitions.