Microwave Spectrum of the Argon-Tropolone van der Waals Complex

The rotational spectrum of the argon-tropolone van der Waals complex in the ground vibrational state has been measured in the frequency range of 6 to 17 GHz using a pulsed-jet, Balle-Flygare-type Fourier transform microwave spectrometer. Eighty-six transitions for the complex (Ar-12C7H616O2) were observed, assigned, and fit using a Watson A-reduction Hamiltonian giving the rotational and centrifugal distortion constants A = 1080.4365(3) MHz, B = 883.4943(3) MHz, C = 749.0571(2) MHz, ΔJ = 2.591(2) kHz, ΔJK = -3.32(1) kHz, ΔK = 5.232(9) kHz, (delta)J = 0.944(1) kHz, and (delta)K = -0.028(8) kHz. The tunneling motion of the hydroxyl proton in the tropolone moiety is quenched in the ground electronic state by complexation with argon. The coordinates of the argon atom in the monomer's principal axis system are a = 0.43 (angstrom), b = 0.23 (angstrom), c = 3.48 (angstrom).