Figure compares the experimental spectrum of (G) 1 (A) 1 (SA) 1 with the spectra of the three lowest energy calculated structures. There are two transitions above 3500 cm -1 with comparable intensities. The free bisulfate O-H stretch of ammonium bisulfate clusters has been observed above 3600 cm -1 while matrix isolation and gas phase FT-IR spectra of G have reported the carboxylic free O-H stretch between 3570 -3590 cm -1 . We assign the carboxylic acid free O-H in the (G) 1 (A) 1 (SA) 1 cluster to the transition centered at 3567 cm -1