The CH3N Diradical: Experimental and Theoretical Determinations of the Ionization Energies

Abstract

Methylnitrene, the CH 3 N diradical, is one of the most interesting of all organic free radicals, and it has drawn a lot of attention in both experiments [1±5] and theory. [6±11] As the simplest alkyl nitrene, the general class of molecules with the form RN, CH 3 N is a dielectronic radical similar to carbene CH 2 : , and is thought to be an important intermediate in many organic and inorganic reactions. [12±14] Berry suggests [1] that the alkyl nitrene should have electron states similar to NH which has been well characterized by spectroscopists. However, much less is known about alkyl nitrenes such as CH 3 N, CH 3 CH 2 ÀN, (CH 3 ) 2 CHÀN, or (CH 3 ) 3 CÀN. There are no reports on the ionization energy of the nitrenes until now, but these ionization energies, especially the first ionization energy, are important physical and chemical data.When combined with ab initio molecular orbital calculations, HeI photoelectron spectroscopy (PES) gives a lot of information on the electronic and vibrational structures, the configuration, the bonding characteristics, as well as the relative photoionization cross sections of different molecular orbitals. Of course, the most important information obtained from the PES study is the ionization energy of the different molecular orbitals. Pople [15] and Ng [16] and their co-workers pointed out that the ab initio Gaussian 2 (G2) calculation can correctly predict the first ionization energy.We have shown how to generate a continuous flowing beam of short-lived species by the microwave discharge or pyrolysis of the parent species, allowing us to perform PES studies on reactive open-shell species such as NO 3 , [17] (CH 3 ) 2 N, [18] CH 3 O, [19] CH 3 S, [19] CH 3 SS, [20] CH 3 CH 2 S, [21] (CH 3 ) 3 CO [22] and further demonstrated that the G2 calculation can also predict the ionization energies of different ionic states. Herein, we present the experimental and theoretical determinations of the ionization energies of different ionic states for the CH 3 N diradical; this is also the first report on ionization energy for the nitrenes.Calculations on the CH 3 N 3 molecule indicate that the bond between the CH 3 N and N 2 units is the weakest present and therefore pyrolysis of the CH 3 N 3 offers a simple route to the CH 3 N diradical through loss of the N 2 unit. [23±26] However, in the pyrolysis study of CH 3 N 3 carried out by Bock and coworkers, [24±26] no PES signals of the CH 3 N diradical could be detected and PES signals attributed to CH 2 NH appeared when CH 3 N 3 was heated to 770 K.Through careful analysis of the experimental process used by Bock et al. [24±26] it is clear that: 1) the distance from the point of pyrolyzation of the parent compound to the photoionized point for the new species generated is too far (maybe more than half meter); 2) the pyrolysis temperature (770 K) for maintaining the new species is also too high. Obviously, it is difficulty to record the PES signals of transient species which have a short life-time, such as the CH 3 N diradical. I...

CAS Calculation of the Excited States of the Methylthio Neutral Radical and Its Ions

“…Our calculated first three 0–0 band adiabatic ionization energies are 9.31, 10.13, and 10.28 eV. The first ionization energy was also obtained vertically as 9.266 eV theoretically, which is close to the adiabatic ionization energy 9.31 eV. So, the nonbonding character can be confirmed to the 3a″ orbital.…”

“…The adiabatic affinity energy of the CH 3 S neutral radical in the CASPT2 level is 1.59 eV. This value is less than 1.861 ± 0.004 eV from the photodetachment spectra experiment and a determination by the photoelectron spectrum. ,, …”

“…This value is less than 1.861 ± 0.004 eV from the photodetachment spectra experiment and a determination by the photoelectron spectrum. 22,23,36 Compared to the homologous CH 3 Se radical, 39 the electronic configuration is similar, and the HOMO is in a′ expression in the C s point group (E expression in C 3v point group) for the CH 3 S radical. The lowest four electronic states are in the symmetry of 2 A′ < 2 A″ < 2 A′ < 2 A″, which is consistent with that of CH 3 Se.…”