The electronic structure of flavin derivatives: Part I. Ab initio calculations for 1H-alloxazine and 10H-isoalloxazine,their reduced derivatives and related compounds; assignments of photoelectron spectra

Ab initio calculations with a (7s3p) basis set are performed on uracil, lumazine, isoalloxazine, its 10-methyl derivative and 1,5-dihydroisoalloxazine. He(I) and He(II) photoelectron spectra of methylated derivatives of these compounds are reported.Comparison of photoelectron spectra with ab initio calculations leads to a new assignment of the uracil photoelectron spectrum. The photoelectron spectra of lumazine and the (iso)-alloxazines are analyzed with the aid of earlier spectra of pyrazine, quinoxaline, o-phenylenediamine and the results for uracil. Combined with the ab initio results the analysis leads to a consistent assignment of the photoelectron spectra.