HIGH-RESOLUTION MICROWAVE SPECTROSCOPY OF IMINOSILICON, HNSI

Abstract

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 $v_2$ are particularly intense, enabling detection of transitions from as high as $(0,22^0,0)$ (i.e. $\sim$10,000~cm$^{-1}$ above ground). At high spectral resolution, well-resolved nitrogen quadrupole structure has been observed in nearly every transition. Excitation of $v_1$ or $v_3$ changes $eQq$(N) little, but $eQq$(N) systematically decreases with increasing excitation of the $v_2$ bend, from a value of 0.376(5)~MHz for $(0,0^0,0)$ to -2.249(5)~MHz for $(0,20^0,0)$. 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.