Selectively excited, wavelength resolved emission spectra of gaseous organic ions

Previously reported laser excitation spectra of a number of gaseous organic ions have characterized the vibrational structure of the excited electronic states, but have given only slight information about that structure in the ground electronic state. We now report wavelength resolved emission spectra induced by laser excitation of specific excited state vibrational levels for C₆H₃F₃⁺ and C₆H ₃Cl₃⁺. These spectra directly characterize the ground state vibrational structure. Excitation of the vibrationless level confirms that previously reported ground state vibrational frequencies obtained for the ions in Ne matrices are characteristic of the isolated molecules. Similar spectra obtained by pumping excited, nontotally symmetric, vibrational levels show directly, for the first time, the split components of the most active Jahn-Teller modes in the ground electronic state. The splittings show that several previous analyses of Jahn-Teller effects in these ions were either incorrect or incomplete, and provide the necessary additional information to perform a complete analysis.