Francoise Pauzat, Julien Pilme, Julien Toulouse, and Yves Ellinger The puzzling difference between the IR spectra of polycyclic aromatic hydrocarbons (PAHs) and those of the corresponding positive ions (PAHs) is a well documented fact, although the basic reason for it is far from clear. In this report, the CH fragment, in its neutral and ionized forms is taken as a ... [J. Chem. Phys. 133, 054301 (2010)] published Mon Aug 2, 2010.