Knowledge Bank

Microwave measurements from 7 to 130 GHz, consisting of 444 rotational transitions in the ground vibrational state of hydrazine with $J\le 31$ and $Ka\le 6$ have been fit to an effective rotational Hamiltonian containing 9 asymmetric rotor constants, $14NH2$ inversion parameters, and 1 internal rotation parameter, with an overall standard deviation of the fit of 0.40 MHz. This set of parameters contains: (i) the three rotational constants; (ii) tunneling splitting constants for $NH2$ inversion at one end of the molecule, for $NH2$ inversion at both ends of the molecule, and for internal rotation through the trans barrier; (iii) three K-type doubling constants affecting the K=1 levels: (iv) an a-type Coriolis interaction with matrix elements linear in K; and (v) various centrifugal distortion corrections. A consistent group theoretical formalism has been used to label the energy levels and to select terms in the rotational Hamiltonian. The Hamiltonian matrix, which is set up in a tunneling basis set, is of dimension $16\times 16$ and contains only $\Delta |K|=0$ matrix elements, asymmetric rotor effects being taken into account on the diagonal by a Polo expansion in $bn$. Hyperfine interactions and force fields (barriers) have not been treated.