DIPOLE-MOMENT ANALYSIS OF EXCITED VAN-DER-WAALS VIBRATIONAL-STATES OFARH35CL

The far-infrared laser electric resonance spectra of the prototypical 'atom-diatom complex (ArHCl)-Cl-35 are analyzed using improved zero-fi eld molecular constants, yielding accurate permanent and transition di pole moments for the three lowest excited van der Waals vibrational st ates. The constants are obtained from a multistate fit to previous mic rowave, far-infrared laser electric resonance, and far-infrared tunabl e laser spectra, as well as new far-infrared measurements of the SIGMA -stretch state, which are reported here. The signs of the dipole momen ts and Coriolis coefficients establish the relative orientations of th e HCl subunit in these states. The fit is found to converge only if th ese signs correspond to the HCl pointing in opposite directions along the a inertial axis in the SIGMA-stretch and SIGMA-bend states. A weak preference, near the experimental error limit, is found for the Ar-Cl -H average angle in the PI-bend state to be greater than 90-degrees, c ontrary to expectation. For the best fit, we obtain the a-axis dipole moment components -0.5413(11) D (SIGMA bend), -0.26345(29) D (PI bend) , and 0.6754(36) D (SIGMA-stretch); and the b-axis components 0.365(12 ) D (PI and SIGMA-bend) and -0.0465(43) D (PI and SIGMA stretches), wh ere the signs of the Coriolis coefficients and mu(a) for the SIGMA str etch have been arbitrarily fixed positive. For the expected PI-bend co nfiguration, with the Ar-Cl-H angle less than 90-degrees, the magnitud es along the a axis change only slightly, but the b-axis components be come 0.149(12) and -0.1403(64) D for the H-SIGMA-bend and PI-SIGMA-str etch interactions, respectively.