THE PURE ROTATIONAL SPECTRA OF ZnO IN THE EXCITED a$^{3}\Pi_i$ STATE

Abstract

The pure rotational spectra of ZnO in the excited a$^{3}\Pi_i$ electronic state have been measured using direct absorption sub-millimeter techniques. This molecule was synthesized by reacting zinc vapor with N$_2$O in the presence of a DC discharge. Nine rotational transitions were recorded for the $^{64}$ZnO, $^{66}$ZnO, and $^{68}$ZnO isotopomers in the v=0 state and data for the main isotopomer was measured in the v=1 state. All three spin components were observed for this state, each exhibiting lambda-doubling. The data were fit with a Hund case(a) Hamiltonian and rotational, spin-orbit, spin-spin, and lambda-doubling constants established. A bond length of 1.8436 \AA{} was determined for this excited state, which is about 0.14 \AA{} larger than that of the ground state.