Binary complexes of HCN with H-2, HD, and D-2 formed in helium nanodroplets

Rotationally resolved infrared spectra have been obtained for HCN-oH(2), pH (2)-HCN, HCN-pD(2), HD-HCN, and oD(2)-HCN binary complexes formed in liquid helium nanodroplets. The isolation provided by the droplets enables us to observe both ortho and para complexes, while in the previous gas phase infr ared study only the more strongly bound J=1 complexes were observed. Of par ticular interest is the observation that the complexes correlating with J=0 and J=1 hydrogen bind to opposite ends of the HCN molecule. In an effort t o understand this behavior we have carried out ab initio calculations at th e CCSD(T) level, exploring the potential energy surface near the correspond ing minima. The dramatic difference between the binding of ortho and para h ydrogen to HCN can be at least partially understood by averaging the calcul ated surface over the appropriate rotational wave functions. <(C)> 2001 Ame rican Institute of Physics.