High resolution infrared spectra of the two "low" frequency intermolecular modes-van der Waals stretch (nu(4)) and geared bend (nu(5)) of (HCl)(2)-have been characterized in HCl-stretch excited states using a slit jet spectrometer. In a high resolution high sensitivity search covering the range between 2880 and 3070 cm(-1) four (HCl)(2) combination bands associated with in-plane vibrations nu(4) and nu(5) have been observed. The vibrational assignment of these bands is based on comparison between observed intermolecular mode energies and predictions from recent six-dimensional (6D) quantum mechanical (QM) calculations [Y. Qiu, J. Z. H. Zhang, and Z. Bacic, J. Chem. Phys. 108, 4804 (1998)], though additional confirmation is provided by ancillary spectroscopic information such as rotational constants, predissociation linewidths, and Cl-35/Cl-37 isotopic band shifts. The experimentally observed intermolecular energies agree with theoretical predictions to approximate to2-4 cm(-1) out of 60-90 cm(-1), suggesting that the 6D potential energy surface can describe combination band excitation in these lower frequency intermolecular coordinates fairly well. Three of the four observed combination bands arise from the upper tunneling level (B+), and all four bands are built exclusively on bound HCl stretch (nu(2)). To account for these striking intensity anomalies, a simple model for three-dimensional QM calculation of transition moments is introduced, which correctly reproduces the experimental trends. In this model, the propensity for nu(2) based combination bands arising from upper tunneling levels can be successfully ascribed to the unusually "floppy" nature of the intermolecular vibrations, which results in a "harmonic oscillator" Deltav=+1 propensity for excitations between tunneling levels along the geared bend coordinate.