THE ROTATIONAL-TUNNELING SPECTRUM OF THE AR-SO2 VANDERWAALS COMPLEX

The microwave spectrum of Ar-SO2 has been observed with a pulsed beam, Fabry-Perot cavity, Fourier transform microwave spectrometer. This complex displays a- and c-type spectra, the latter of which is shifted by internal motion of the SO2 unit. In addition to the spectrum of the normal isotopic form, we have observed the spectrum of Ar-34SO2. Rotational analysis of each spectrum provides the constants A = 9151.235(5) MHz, 1 2(B + C) = 1402.0444(3) MHz, and B - C = 167.808(2) MHz for the normal species, and A = 9112.734(6) MHz, 1 2(B + C) = 1385.149(6) MHz, and B - C = 162.838(2) MHz for the Ar-34SO2 species. Constants relevant to the Coriolis coupling between the tunneling motion and the overall rotation of the molecule are also determined and, along with the rotational constants, make possible an unambiguous determination of the angle between the a axis of the complex and the C2 axis of the SO2 molecule. © 1991.