Angle-resolved thermal desorption of atoms from solid surfaces: one-phonon mechanism

A model for one-phonon thermal desorption is presented in which the structure of the substrate phonons, expressed as a projection on a surface atom of the phonon density of states, appears as a separate factor in the angle- and energy-resolved desorption rate. Desorption from both localized, and delocalized initioladatom states is considered. Under certain circumstances one can obtain the cosine-distribution of the equilibrium theory, but in general, the desorption flux from delocalized states deviates from the cosine law by being peaked away from the surface normal, whereas for localized initiol states, the flux is concentrated more in the normal direction.     

Investigation of the effect of a dc glow discharge on the performance of a particle beam liquid chromatography/mass spectrometry interface

A low voltage (180-V) dc glow discharge device was inserted just below the pneumatic nebulizer in a particle beam interface of a high performance liquid chromatography/mass spectrometry system. The discharge in a helium atmosphere increased the signal produced by 12 test compounds by factors of about 2–6. The increases in signal were probably produced by an increase in the efficiency of solute transmission through the interface. The signal increases caused by the glow discharge were compared to somewhat larger increases caused by 0.01-M ammonium acetate in the mobile phase. The combination of glow discharge and ammonium acetate provided no meaningful advantage over the individual techniques. The mechanism of improved transport efficiency is not proven, but the neutralization of charged particles is a viable hypothesis.     

Amending cultures of selenium-resistant bacteria with dimethyl selenone

A possible biological intermediate in the reduction and methylation of selenium oxyanions, dimethyl selenone, was synthesized, and the first experiments involving the amendment of selenium resistant bacterial cultures with this compound are reported. The amount of volatile, reduced selenium-containing species released from these cultures into the headspace is significantly more than that produced in analogous experiments involving sodium selenate amended cultures. Dimethyl selenone is reduced in the presence of dimethyl sulfide and dimethyl disulfide in a complex growth medium, trypticase soy broth with 0.1% nitrate. This reduction occurs whether or not the reduced sulfur compounds are biologically produced.