The optical-optical double-resonant multiphoton ionization (OODR-MPI) spectrum of NO<sub>2</sub> molecule in the 460-605 nm wavelength region of the probe photon is presented. The mechanism of the OODR-MPI of NO<sub>2</sub> molecule is analyzed. The results show that the resonant features can be assigned to the transitions from the first 3s'sigma'g Rydberg intermediate resonant state to the final np'sigma'u Rydberg series. The ionization pathway is NO<sub>2</sub>(X2A1)-[3h'nu'1]->3s'sigma'g-[h'nu'2]->np'sigma'u-[h'nu'2 or autoionization]->NO<sub>2</sub>(+)+e. It is found that the converging potential of the np'sigma'u Rydberg series and the quantum defect of np orbit about NO<sub>2</sub> are (78803±14) cm<sup>-1</sup> and 0.652±0.014, respectively. The bending vibration frequency of 5p'sigma'u state is determined also.
© 2007 Chinese Optics LettersPDF Article