SUB-DOPPLER SPECTROSCOPY OF AMMONIA NEAR 570 GHZ

We have employed the Cologne terahertz spectrometer [1, 2] to observe Lamb dip and crossover phenomena in rotational spectra at 572 GHz. Bec ause of the large power output of the backward wave oscillators used i n the system, no special means are required to induce this saturation effect; the coincidentally reflected radiation from the bolometer pres ent in our quasi-optical absorption cell is sufficient to saturate the v(z), = 0 sub-group. This effect has allowed the observation of the t hree previously unresolved hyperfine components of the (NH3)-N-14 A <- - S, J(K) = 1(0) <-- 0(0) transition, and was also observed for the an alogous (NH3)-N-15, transition in natural abundance (i.e. 0.366 %). Th ese measurements indicate a possible improvement of molecular transiti on frequencies in the submillimeter region.