Observation of ultraviolet rotational band contours of the DNA base adenine: Determination of the transition moment

Abstract

We report the first observation and analysis of rotational band contours of the jet-cooled DNA base adenine for three vibronic bands at 36 062, 36 105, and 36 248 cm(-1). The lowest n pi* and pi pi* states have been labeled with their excited-state vibronic symmetry, and a strong pi pi*-n pi* vibronic coupling via an out-of-plane vibrational mode has been revealed. The rotational band contours have been recorded by resonant two-photon ionization (R2PI) and analyzed by a genetic algorithm (GA) based fit to obtain the optimum band parameters. The vibronic band at 36 062 cm(-1) shows dominant c-type character with transition dipole moment (TDM) components mu(2)(a):mu(2)(b):mu(2)(c)=0.09: 0.17:0.74 and those at 36 105 and 36 248 cm(-1) show abc-hybrid character with predominantly in-plane TDM components. The band at 36 062 cm-1 has been assigned as the n ->pi* transition, and the 36 105 cm(-1) band as the pi ->pi* transition by the symmetry analysis. The band at 36 248 cm(-1) provides evidence of the strong pi pi*-n pi* vibronic coupling via an out-of-plane vibrational mode.