INVESTIGATION OF THE GROUND VIBRATIONAL-STATE STRUCTURE OF (HCL)-CL-35 TRIMER BASED ON THE RESOLVED K-SUBSTRUCTURE, J-SUBSTRUCTURE OF THE NU(5) VIBRATIONAL BAND

The high resolution rovibrational IR spectrum of the antisymmetric (HCl)-Cl-35 stretching nu(5) vibrational band in the ((HCl)-Cl-35)(3) isotopomer of the trimer has been measured with a tunable infrared diode laser supersonic jet spectrometer. One of the most prominent features of the spectrum is a series of strong lines each formed with P-p or (r)R transitions, with resolved K, J substructure developing between two adjacent P-p or (r)R heads. Analyzing the spectrum of ((HCl)-Cl-35)(3) as the perpendicular band of an oblate symmetric rovibrator, the following molecular parameters have been obtained: nu(0)-C'zeta = 2809.77698(6) cm(-1), B'' = 6.80414(55) x 10(-2) cm(-1), B' = 6.85943(55) x 10(-2) cm(-1), C'-C'' = 2.737(78) x 10(-4) cm(-1), D-JK'' = -8.40(38) x 10(-7) cm(-1), D-JK' = -8.14(38) x 10(-7) cm(-1), D-J'' = 4.26(16) x 10(-7) cm(-1), D-J' = 4.16(16) x 10(-7) cm(-1), D-K'' = 4.32(22) x 10(-7) cm(-1), D-K' = 4.16(22) x 10(-7) cm(-1). A relationship among the centrifugal distortion constants establishes that the geometry of ((HCl)-Cl-35)(3) is consistent with a dynamically averaged planar ground vibrational state. The centers of mass of the (HCl)-Cl-35 components are separated by 3.693(1) Angstrom in this structure. Ab initio methods were also used to estimate the splitting due to the tunneling motions between clockwise (cw) and counterclockwise (ccw) identical structures. Both theoretical and experimental evidence indicate that the (HCl)(3) complex has a planar equilibrium structure with no observable tunneling probability between the cw and ccw forms, thus the molecular symmetry group of the complex is proposed to be C-3h(M).