HYPERFINE INTERACTIONS IN THE NU(3) BAND OF OSMIUM-TETROXIDE - ACCURATE DETERMINATION OF THE SPIN ROTATION CONSTANT BY CROSSOVER RESONANCE SPECTROSCOPY

A series of three papers is devoted to a detailed presentation of the hyperfine interactions in the nu3 band of OsO4. In this first paper, we emphasize the experimental aspects although a first theoretical approach of the hyperfine problem is given. Several recording techniques with a resolution of about 1 kHz have enabled us to measure very precisely a set of hyperfine structures of (OsO4)-Os-189 and (OsO4)-Os-187. The oservation crossover resonances, with high-J values, gave access to an independent determination of the hyperfine structures in the lower and upper levels. As a consequence, hyperfine constants are determined very accurately. This is illustrated by the determination of the spin-rotation constant of the two isotopic species: C(a)(OsO4)-Os-189 = -21.6891(33) kHz and C(a)(OsO4)-Os-187 = -6.379(20) kHz, and the isotopic relation is verified with a relative precision of 3 x 10(-3). In addition, we report a grid of absolute frequencies of 70 fundamental lines with an accuracy ranging from 50 Hz to 2 kHz. (C) 1994 Academic Press, Inc.