Electronic absorption spectra of radical cations of 1-methyl, 2-methyl and9-methyl anthracenes

Electronic spectra of radical cations of 1-methyl anthracene, 2-methyl anth racene and 9-methyl anthracene are investigated. The ions were produced by photoionization of the hydrocarbons in boric acid matrix. The electronic ab sorption spectra. of 1-methyl anthracene cation and 2-methyl anthracene cat ion are reported for the first time. For interpretation of the spectra, ZIN DO/S-CI calculations are carried out. The bathochromic shifts of the spectr al bands of the ionized methyl anthracenes from those of antracene cation a re attributed to "conjugative" effect. The 442 nm, electronic band of 2-met hyl anthracene cation and 638 nm and 698 nm spectral bands of 9-methyl anth racene cation are found to be in close proximity with the diffuse interstel lar bands (DIBs) at 443 nm, 638 nm and 699 nm. This observation leads us to speculate the possibility of the existence of these ionic species in the i nterstellar matter.