Distinguishing the 7H and 9H tautomers of 2,6-dAP, An initial R2PI scan of 2,6-dAP served to identify resonant vibronic transitions. We observed two distinct regions of the spectrum, offset by ~2500 cm -1 (see below). Using IR-UV mode I and mode II (see Figures ) we confirmed the presence of both the 7H and 9H tautomers, in accordance with earlier work by Gengeliczki et al.( )