Controlling molecular fragmentation of diazodiarylmethanes using low energy electrons from 17 to 70 eV

Diazo compounds are light sensitive, they are widely used in synthetic chemistry and photochemistry as well as in polygraph y, UV lithography and reprography. At the present time methods of electron lithography are being intensive developed. It can be assumed that diazocompounds will be applied also in electron lithography. For the study of radiolytic processes in electron-impact mass spectrometry is suitable, first of all for processes run in gaseous phase. It is known that fragmentation, intensity and contribution of fragment ions depend strongly on the energy of ionizing electrons. The electron-impact-induced fragmentation (the mass spectra, 17 - 70 eV) of diazodiarylmethanes was studied. As a suitable compound were selected the following diazodiarylmethanes: diazodiphenylmethane, Ia; phenyl-para-methoxyphenyldiazomethane, Ib; phenyl-para-biphenyldiazomethane, Ic; 10-diazonaphtoquinone, Id; and 9-diazothiaxanthene, Ie). The mass spectra were measured using Varian MAT 111 instrument with direct introduction of samples, with a source temperature of 120 deg C, energy of ionising electrons in the range 17 - 70 eV and 150 μA and sample reservoir laboratory temperature. The elimination of diazo group is a typical reaction for fragmentation of diazocompounds after ionisation of molecules with electron impact. All investigated diazodiarylmethanes at 70 eV show the molecular ion with 1.6 - 30.4 % of relative abundance. Besides formation of typical ions [M-N₂]^+· we registered formation of non-conventional typical fragments [M-C]⁺, [M-N]⁺, [M-C-N]⁺ and [M-C-N₂]⁺. Doubly-charged ions were also observed. The abundance of fragmentation ions diminishes with decrease of energy of ionizing electrons. Dependence of relative abundance of ions on energy of electron beams we registered on 3D EI-MS spectra. For all investigated diazocompounds we proposed corresponding fragmentation schemes. At the energy of ionising electrons ∼20 eV the dominating ions are [M-N₂]^+·. (authors)