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Lifetimes of individual Na2 ro-vibrational levels of the 21Σ + u double well-state have been measured using a delayed photoionization technique. Ground state Na2 produced in a molecular beam is excited resonantly by the doubled output of a pulsed dye laser in the range 333 – 357 nm and then ionized by a 532 nm photon from a time-delayed Nd:YAG laser. By appropriate excitation laser tuning and systematic variation of the probe laser delay, ro-vibrational level resolved lifetimes are obtained for v=25- 49. The double well state lifetime values are found to decrease from about 50 ns at v=25 to about 40 ns near the barrier at around v=33 and then to increase back to about 50 ns at the highest observed level of v= 49. We have also performed lifetime calculations using the Leve8 and Bcont programs by Leroy1 , the latter in a version modified by Brett McGeehan. We find that including only bound-bound transitions, the theoretical lifetime values are too large by a factor of up to 2. Inclusion of pertinent bound-free transitions improves the agreement noticeably. 1 R. J. Le Roy, LEVEL 8.0: A Computer Program for Solving the Radial Schr¨odinger Equation for Bound and Quasibound Levels, University of Waterloo Chemical Physics Research Report CP-663 (2007); see

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