Showing papers in "Transactions of The Faraday Society in 1963"

Mass spectrometric and knudsen-cell vaporization studies of group 2B-6B compounds

Abstract: The vaporization of the nine compounds of Zn, Cd and Hg with S, Se and Te has been investigated by mass spectrometry. The typical process is the decomposition into gaseous metal atoms and diatomic group 6B molecules. Small amounts of polymeric species of sulphur were observed in the vapour above HgS and considerable amounts of polymeric selenium molecules above HgSe; HgTe yields Hg(g) and solid Te. No gaseous group 2B-6B molecules were observed; their concentration is below 1 part in 103-105. Estimates of dissociation energies are made and the possibility of observing these molecules is discussed. Decomposition pressures of all nine compounds were measured by the Knudsen method and corresponding enthalpy and entropy data deduced and compared with literature data. The heat of vaporization of lead has been remeasured. The heats of atomization of the group 2B-6B compounds are compared with those of isosteric compounds and elements, and the trends are discussed.

Structural studies of linear molecules by microwave spectroscopy

Abstract: : Rotational constants were measured for several isotopic forms of fluorine cyanide and fluoro acetylene. Accurate bond-distances were computed for all the halogen cyanides and for fluoro- and chloracetylene, by the method of isotopic substitution at all atoms (except F and I). The CF bonds in these compounds are the shortest yet found. The CN distance is virtually constant at 1.159 A. The nuclear quadrupole coupling constant for nitrogen-14 in fluorine cyanide, -2.67 Mc/s, is the lowest yet measured for a cyanide grouping. The dipole moments of fluorine cyanide and fluoroacetylene, from Stark effects, are 2.17 D and 0.75 D respectively. Rotation spectra of molecules in excited bending vibrational states were analysed for fluorine cyanide, fluoroacetylene and cyanoacetylene.

Enthalpy of hydration of the proton

Abstract: A method is presented for estimating the absolute hydration enthalpy of the proton at infinite dilution and at 298 c- K. The method makes use of a simple model of aqueous solutions, and is based on the significance of differences between thermodynamic hydration functions for ions of opposite charge. Values of the differences between conventional hydration enthalpies are plotted against (R + alpha )/sup -3/, where R is the effective radius of the ion and alpha is the effective radius of the water molecule. This plot yields the absolute hydration enthalpy of the proton. The value obtained is -260.7 kcal mole/sup -1/ with an estimated uncertainty of surface proces 2.5 kcal mole/sup - 1/. An estimate of the quadrupole moment of the water molecule is also made. (auth)

High-resolution N.M.R. spectra in electric fields

Abstract: A general method of calculating high-resolution nuclear magnetic resonance spectra of polar fluids in electric fields is described. The partial orientation of the molecular electric dipole moments in a strong electric field modifies the averaging of the tensors representing nuclear magnetic shielding and spin-spin coupling. An effective Hamiltonian for polarized fluids is deduced and used to predict spectral changes in certain standard types of n.m.r. spectra involving spin-1/2 nuclei. Equivalent nuclei are found to produce splittings propotrional tot he inverse cube of their separation. (auth)

Catalysis by Brönsted bases of the reaction between CO2 and water

Abstract: The catalysis of the reaction CO2+H2O→HCO−++H+ by a number of anions has been studied at 0°C. Anions which have a negatively-charged oxygen atom and at least one hydroxyl group attached to the same central atom, and in which the negative charge is not delocalized by resonance effects, form a single group which obeys the Bronsted relationship. Anions of other types are in general weaker catalysts for a given pK.