Optical-Optical Double Resonance MPI Spectroscopic Investigation of Iodine Molecule

Using optical-optical double resonance multiphoton ionization（OODR-MPI）spectroscopy,we have measured and analyzed the transition pathways,the ion-pair state and the rotational energy relaxation in I₂.In our measurement of the OODR spectra of I₂,using lasrs of wavelength～532nm ＆ 590-610nm,aregular progression with a spacing of 37 cm^-1and total energy at 53000cm^-1 has been recorded.By varing the delay time between the two dye lasers and by measuring the dependence between the MPI signal and the laser power,the transition pathway of the five-photons ionization is determined to be the（1+2+2）process of F-B-X and the upper resonance state is identified as the highly excited vibrational levels in the F（O⁺u） state arising from the ions I⁺（³P（_1,0））+I^-（¹S）.Finally,the rotational energy relaxation in the B∏（O⁺u）state is measured with the F（O⁺u）as the probing state and the broadening of the spectral lines is discussed.