Conformation-specific ultraviolet spectroscopy of benzo-18-crown-6 complexes with a potassium cation

We investigate conformation-specific UV spectra of benzo-18-crown-6 complexes with a potassium cation using a UV–UV hole burning (HB) technique developed for ions in a quadrupole ion trap. Three different UV–UV HB spectra are obtained: two spectra represent the electronic spectra of conformers, K-a and K-b, respectively, and the third exhibits the transitions of a vibrationally ‘hot’ K-b conformer. These demonstrate that the UV–UV HB technique, of which the applicability was first tested only for ions of a single isomer, can be used to differentiate vibronic peaks of ions existing as two or more different conformers including their vibrationally ‘hot’ species.