  We present spectra of the 3.3 $\mu$m and 11.2 $\mu$m PAH features of a large
number of (extra-) galactic sources, obtained with ISO-SWS. Clear variations
are present in the profiles of these features. The sources are classified
independently based on the 3.3 and 11.2 $\mu$m feature profiles and peak
positions. Correlations between these classes and those based on the 6--9
$\mu$m features (Peeters et al. 2002) are found. Also, these classifications
depend on the type of object. The observed pronounced contrast in the spectral
variations for the CH modes (3.3 and 11.2 $\mu$m bands) versus the CC modes
(6.2, 7.7 and 8.6 $\mu$m bands) is striking : the peak wavelengths of the
features attributed to CC modes vary by $\sim$15--80 cm$^{-1}$, while for the
CH modes the variations are $\sim$4--6.5 cm$^{-1}$. We summarize existing
laboratory data and theoretical calculations of PAH molecules and complexes. In
contrast to the 6.2 and 7.7 $\mu$m components which are attributed to PAH
cations, the 3.3 $\mu$m feature appears to originate in neutral and/or
negatively charged PAHs. We attribute the variations in peak position and
profile of these features to the composition of the PAH family. The variations
in FWHM of the 3.3 $\mu$m feature remains an enigma while those of the 11.2
$\mu$m can be explained by anharmonicity and molecular structure. The possible
origin of the observed contrast in profile variations between the CH modes and
the CC modes is highlighted.
