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We measure the J = 1 to J = 2 fine structure interval in the ( 3)2P state of helium to be 2 291 175.9(1.0) kHz. We use laser excitation of an atomic beam along with an integrated electro-optic modulator technique to obtain this result. The result is consistent (2.9+/-3.2 kHz) with what could be considered an earlier version of this experiment but is not in good agreement ( 20+/-5 kHz and 22+/-8 kHz) with the two other precision determinations of this interval. The current theoretical prediction lies between and overlaps the experiments.

We measure 31,908,131.25(30) kHz for the 2(3)}P J=0 to 2 fine structure interval in helium. The difference between this and theory to order mα7 (20 Hz numerical uncertainty) implies 0.22(30) kHz for uncalculated terms. The measurement is performed by using atomic beam and electro-optic laser techniques. Various checks include a 3He 2{3}S hyperfine measurement. We can obtain an independent value for the fine structure constant α with a 5 ppb experimental uncertainty. However, dominant mα8 terms (potentially 1.2 kHz) limit the overall uncertainty to a less competitive 20 ppb in α.

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In a recent laser spectroscopic study of the H2, D2, and HD molecules [J. M. Gilligan and E. E. Eyler, Phys. Rev. A 46, 3676 (1992)],the energies of transitions between the X 'Xg+ ground state and the metastable EF 'Xg+ state were measured precisely with respect to seven transitions in the iodine molecule.We report the absolute wavelengths of these iodine transitions with an accuracy of 250 kHz (5 parts in 10 ) by interferometric comparison with the iodine-stabilized He-Ne standard at 633 nm. The full accuracy of the transitions to the EF state can now be realized. Improved ionization potentials for H~, D2, and HD are obtained using these results in combination with other previous measurements connecting the EF state to high Rydberg states. These ionization potentials are generally, but not completely, in agreement with ab initio theory. We also compare our measurements of the iodine wavelengths with less accurate values predicted from previously determined empirical molecular constants of the iodine B~X transition. We discuss the possibility of determining these constants more accurately and thereby improving the overall accuracy with which the widely used visible and near-infrared spectrum of I2 is known.PACS number(s): 33.20. Kf, 35.20.Vf, 06.20.Hq

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