ISSN 0020-4412, Instruments and Experimental Techniques, 2013, Vol. 56, No. 1, pp. 76–79. © Pleiades Publishing, Ltd., 2013. Original Russian Text © N.L. Asfandiarov, S.A. Pshenichnyuk, V.S. Fal’ko, G.S. Lomakin, 2013, published in Pribory i Tekhnika Eksperimenta, 2013, No. 1, pp. 87–90. 76 INTRODUCTION The electron transmission spectroscopy (ETS) method [1] is intended to measure vertical attachment energies (E VA ) of electrons by molecules in the gas phase. It is common practice to associate these ener- gies with energies of vacant molecular orbitals or, more strictly, with short-lived states of molecular negative ions (resonances in the full cross-section for scattering of electrons by molecules) [2]. The energy widths of the corresponding resonance states are related to their extra electron mean autodetachment lifetimes. Thus, the ETS method gives unique information on electron structures of molecules and properties of correspond- ing short-lived resonance states of negative ions. The practice showed that the simplest and conve- nient design of an electron gun that creates an electron beam with a varied energy is the so-called trochoidal monochromator [3]. The principle of operation of this unit consists in transmitting an electron beam through crossed electric and magnetic fields as a result of which a spatial electron velocity dispersion arises. Cutting by lenses with holes a part of the dispersed beam, one can obtain a quasi-monochromatic electron beam [3, 4]. To increase the recording system sensitivity and convenience of estimating the peak half-height reso- nance width, it is agreed to modulate the electron energy by a small sinusoidal voltage, which is created in a collision chamber by a special cylindrical elec- trode. As a result, the derivative of the current of trans- mitted electrons (which were not scattered on mole- cules of the studied substance) is recorded at the unit output as a function of their energy , where I(E) is the current of electrons, and E is their energy. The energy distance between the minimum (E dip ) and maximum (E peak ) of the corresponding resonance is taken as a peak half-width (see Fig. 1). The position of ( ) - ( ) dI E dE the peak of the second derivative I(E) with respect to the energy corresponds to the resonance maximum (E VA ). The information on energies of vacant molecular orbitals is demanded by needs of quantum chemistry, physics of low-temperature plasma, chemical physics, etc. One should separately note a close interrelation of methods of ETS and dissociative electron attachment mass-spectrometry [5, 6]. The first method supplies information on the full cross section for scattering of electrons on molecules, and the second method pro- vides information on partial cross sections of dissocia- tive electron attachment to molecules. Therefore, the GENERAL EXPERIMENTAL TECHNIQUES An Electron Transmission Spectrometer with a Trochoidal Electron Monochromator N. L. Asfandiarov*, S. A. Pshenichnyuk, V. S. Fal’ko, and G. S. Lomakin Institute of Physics of Molecules and Crystals, Ufa Scientific Centre, Russian Academy of Sciences, pr. Oktyabrya 151, Ufa, 450075 Russia *e-mail: nail_asf@gmail.com Received January 19, 2012 Abstract—The design of an electron transmission spectrometer is described and test measurement results for naphthalene, 1,3-dichlorobenzene, and phenylacetylene molecules are given. The trochoidal electron monochromator allows one to reach a 30-meV resolution at a half-height volt–ampere characteristic. DOI: 10.1134/S002044121301003X –dI(E )/dE E el , eV E dip E peak E VA2 E VA1 Fig. 1. Typical appearance of the electron transmission spectrum.