High-resolution rotational spectroscopy of iminosilylene, HNSi

By means of Fourier transform microwave spectroscopy of a supersonic beam, the fundamental rotational transition of isotopic and vibrationally excited iminosilylene, 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 nu(2) are particularly intense, enabling detection of transitions from as high as (0,22(0),0) (i.e. similar to 10,000 cm(-1) above ground). At high spectral resolution, well-resolved nitrogen quadrupole structure has been observed in nearly every transition. Excitation of nu(1) or nu(3) changes eQq(N) little, but eQq(N) systematically decreases with increasing excitation of the nu(2) bend, from a value of 0.376(5) MHz for (0,0(0),0) to -2.257(5) MHz for (0,20(0),0). With the large amount of new data in hand, it has also been possible to determine the leading vibration-rotation constants (alpha(i) and gamma(i)) for nu(2) or nu(3) to high precision, and derive a revised semi-empirical equilibrium structure for this fundamental triatomic molecule. Various electronic and molecular properties of iminosilylene have been calculated at the coupled cluster level of theory, and these generally agree well with experiment and previous calculations. An unsuccessful search for HSiN, a highly polar isomer calculated to lie nearly 3 eV above HNSi, is also reported.