Inelastic collisions of the uracil molecules with electrons

Abstract

Ionization and excitation of the uracil molecules by electron impact is investigated. Production of positive ions of uracil molecules (nucleic acid base) was studied using a crossed electron and molecular beam technique. The method developed by the authors enabled the molecular beam intensity to be measured and the electron dependences and the absolute values of the total cross sections of production of both positive ions to be determined. It is shown that the total positive uracil ion production cross section reaches its maximal value of (1.0 ± 0.1) × 10(-15) cm(2) at the 95 eV electron energy. Dissociative ionization cross sections were also determined. The luminescence spectra of isolated uracil molecules in the wavelength range of 200-500 nm under the influence of slow electrons are obtained. In the spectrum, more than 20 spectral bands and lines at 100 eV electron energy are observed. It is shown that the uracil radiation spectrum is formed by the processes of molecules dissociative excitation, dissociative excitation with ionization, excitation of electronic levels of the initial molecule and molecular ion.

Communication: Electron ionization of DNA bases

“…Our measurements on uracil 29 have also stressed the need for measurements on the DNA bases, as they gave cross sections about a factor of two larger than previously reported. 26 The limited absolute partial cross sections [23][24][25] that have been reported are also susceptible to similar uncertainties as in the total ion cross sections.…”

“…The available theoretical [13][14][15][16][17][18][19] and measured [20][21][22][23][24][25][26] cross sections are also shown in the figure. The measurements [23][24][25][26] used a crossed beam method and the absolute cross sections were obtained directly by measuring the total ion current, the target beam density, and the volume overlap between the beams using the geometrical details of the setup. The most striking part of the results is the difference between the present and the previous measurements.…”

“…Even the large difference between the theory and these measurements does not show any consistency, though all of them have been made using the same experimental setup. [23][24][25][26] As a general thumb rule, for a given class of molecules like the DNA bases, one expects the cross sections to scale with the size of the molecule or molecular mass. The measured cross sections fail to conform to this thumb rule as they range from 8 A 2 for cytosine (mass = 111 amu) to 32 A 2 for guanine (mass = 151 amu).…”

“…[20][21][22] So far, there exists only one set of absolute cross section measurements. [23][24][25][26] These measurements, carried out up to 200 eV of impact energies, vary from theory by a factor of 0.5-2 depending on the molecule. Even the large difference between the theory and these measurements does not show any consistency, though all of them have been made using the same experimental setup.…”

The luminescence of guanine molecules in the gas phase under the electron beam

“…Спекральна лінія з довжиною хвилі λ = 486,1 нм належить атому гідрогену (Нβ серія Бальмера) і, до речі, спостерігається у спектрах інших азотистих основ [7]. Звідси випливає важливий фізичний висновок, що під дією електронів у біоструктурах утворюється значна кількість атомів гідрогену.…”