The microwave spectrum of tert-butyl isocyanate

Abstract

The rotational spectrum of tert-butyl isocyanate, (CH 3) 3C-NCO, has been assigned using pulsed molecular beam microwave Fourier transform spectroscopy. The rotational constants are A = 4572.6 MHz (assumed), B = 1632.948 (15) MHz, C = 1630.493 (14) MHz; the barrier to internal rotation of the tert-butyl group (assumed to constitute a symmetric internal rotor, the NCO group forming the frame) is V 3 = 41.510 (15) cm −1, the moment of inertia of the internal top is I α = 111.388 (4) amu · A ̊ 2 , and the angle between the internal rotor axis and the a-principal inertia axis is θ = 24.169 (3)°. The nitrogen nuclear quadrupole coupling constants are χ aa = +2.6376 (4) MHz, χ bb = −1.4935 (7) MHz, χ cc = −1.1441 (7) MHz, χ ac = +0.1731 (15) MHz (the molecule has an ac-plane of symmetry). The principal elements of the coupling tensor are χ zz = +2.6455 MHz, χ xx = −1.4935 MHz, χ yy = −1.1520 MHz; the angle between both axis systems is 〈( az) = +2.615° (with the x-axis perpendicular to the symmetry plane).