On the hyperfine structure of NO2 levels near dissociation threshold

We report the first direct measurement of the hyperfine structure of single NO2 molecular eigenstates in the 2.53 cm(-1) region below dissociation threshold (D-0), using the method of polarization quantum beat spectroscopy (QBS). The hyperfine interaction of these loosely bound states is substantially weaker (on the average by a factor of similar to 5) than found at energies below 22 000 cm(-1), but is similar on the average to that observed 50-150 cm(-1) below threshold. The implications of our results regarding the participation of additional electronic states near D-0 are discussed. (C) 2000 American Institute of Physics. [S0021-9606(00)01423-9].