Excitation of L-valine molecules by electrons and photons

Excitation of L-valine molecules was studied by optical spectroscopy. Optical emission spectra of the L-valine molecule and optical excitation functions of molecular bands and the Hβ spectral line were measured in the gas phase using electron impact. In the spectra of optical emission in the wavelength range of 250–500 nm, intense emission bands were found at energies of incident electrons of 30, 50 and 70 eV. Analysis of structural features of the valine molecule suggested a fragmentation scheme with the formation of excited particles in collisions with electrons. A notable feature of the presented optical excitation functions is a different growth dynamics with an increase in the energy of exciting electrons and the presence of a number of features and kinks, which are especially pronounced for λ = 305 nm and λ = 311 nm. The excitation thresholds were determined from the initial sections of the excitation functions of the most intense spectral lines by the least-squares method. The photoluminescence spectra of L-valine were measured for the first time on a Shimadzu RF-6000 spectrofluorophotometer in the spectral range of 400–800 nm for excitation wavelengths of 250, 275, 333, 351, and 380 nm

Ionization and fragmentation of valine molecules in the gas phase by electron impact

Formation of fragment ions due to single and dissociative ionization of the valine molecule ($$\hbox {C}_{{5}}\hbox {H}_{{11}}\hbox {NO}_{2})$$ by electrons was studied by mass spectrometry. This is the first experimental mass-spectrometric measurement of total cross-section in arbitrary units of the valine molecule ionization by electron impact. The experiment was carried out using a setup with an MX-7304A monopole mass spectrometer in the range of mass numbers of 0–120 Da. Mass spectra of the molecules were studied at different vapor temperatures. The results obtained were compared with the mass spectra of the D-, L-, and DL-enantiomeric forms of the valine molecule taken from NIST and SDBS databases. The features of the processes of fragment ion formation of valine molecules by electron impact were analyzed in detail. Dynamics of the fragment ion yield in the range of the initial substance evaporation temperatures of 300–440 K was studied. The ionization potential of the valine molecule was measured ($$8.72\pm 0.22~\hbox {eV}$$) and calculated ab initio in the adiabatic approximation (9.367 eV). The ionization potential was estimated from the binding energy of the HOMO orbital of the neutral molecule. This is the first calculation of the single ionization cross section of the D-, DL-, and L-forms of this molecule in the Binary-Encounter-Bethe model and using the Gryzinski formula. The experimental cross section values at the threshold are normalized by the theoretical values in absolute units