* K. HARADA*, Y. IWASAKI, T. GIESEN AND K. TANAKA, Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashiku, Fukuoka, 812-8581 JAPAN.

~~~~H_{2}-H_{2}O is a weakly bound complex and it has a various states according to the internal rotation for both H_{2} and H_{2}O moieties. In our previous study, we have reported the pure rotational transitions of the (o)H_{2} complex in the ground H_{2}O rotational state, 0_{00}(
), for both H_{2}-H_{2}O and H_{2}-D_{2}O, where (o)H_{2} (j_{ H2} =1) is rotating perpendicular to the intermolecular axis to give the projection of j_{ H2} to the axis k_{ H2} to be zero (i.e.
state).

~~~~In the present study, we have observed the rotational transitions for the 0_{00} (
) states in the millimeter-wave region up to 220 GHz, where the (o)H_{2} is rotating around the intermolecular axis to give the projection k_{ H2} to be one (i.e.
state). The center of mass bond lengths derived from the observed rotational constants for 0_{00} (
) are longer by 5 % than those for 0_{00} (
), while force constants for the intermolecular stretching for 0_{00} (
) derived from centrifugal distortion constants are smaller by 23 % than those for 0_{00} (
), suggesting the
and
substates have quite different structures.

~~~~The recent theoretical calculation indicates that for 0_{00}(
), (o)H_{2} is bound to the oxygen site of H_{2}O, while for the 0_{00} (
) state, (o)H_{2} to the hydrogen site of H_{2}O, and the 0_{00}(
) state is by 14 cm^{-1} more stable than the 0_{00} (
) state. Observed molecular constants for 0_{00}(
) and (
) are consistent with the structures given by the theoretical calculation. ~~~~We also observed the rotational spectrum in the 1_{01} (
) and (
) states, where
and
correspond to the rotation of H_{2}O perpendicular and parallel to the intermolecular axis and (o)H_{2} is calculated to be bound to the oxygen site of H_{2}O. The energy difference between the 1_{01} (
) and (
) states will be discussed due to the Criolis interaction between these substates.