15min:

M. C. MCCARTHY, P. THADDEUS, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, U.S.A. and School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138, U.S.A.; FILIPPO TAMASSIA, Dipartimento di Chimica Fisica ed Inorganica, Universitá di Bologna, V.le Risorgimento 4, I-40136 Bologna, Italy; S. THORWIRTH, Max-Planck-Institut für Radioastronomie, 53121 Bonn, Germany, and I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.

By means of Fourier transform microwave spectroscopy of a supersonic beam, the fundamental rotational transition of isotopic and vibrationally-excited iminosilicon HNSi has been detected. In addition to seven isotopic species, vibrational satellite transitions from more than 30 vibrationally-excited states, including the three fundamental modes, have been detected. Those from v₂ are particularly intense, enabling detection of transitions from as high as (0,22⁰,0) (i.e. 10,000~cm^-1 above ground). At high spectral resolution, well-resolved nitrogen quadrupole structure has been observed in nearly every transition. Excitation of v₁ or v₃ changes eQq(N) little, but eQq(N) systematically decreases with increasing excitation of the v₂ bend, from a value of 0.376(5)~MHz for (0,0⁰,0) to -2.249(5)~MHz for (0,20⁰,0). With the large amount of new data in hand, it has been possible to determine more precise vibration-rotation constants and an improved semi-empirical structure for this triatomic molecule. An unsuccessful search for HSiN, a highly polar isomer calculated to lie nearly 3~eV above HNSi, is also reported.