One thing that shows up brightly in all of the VIMS and camera images is a
shifting complex of clouds near Titan's south pole. These clouds were initially
assumed to be methane, but Porco mentioned that the VIMS team had doubts. Brown
confirmed that there was "something going on" in the south polar region,
indicating that the clouds may not be methane. He said the VIMS team had noticed
that the clouds became brighter as VIMS looked at them in longer wavelengths,
indicating that the clouds were made of relatively large particles bigger than 5
microns in diameter.

INMS Team Leader Hunter Waite reported the detection of molecules that
scientists already knew were in Titan's upper atmosphere, namely nitrogen and
methane. But they were shocked to see more complex hydrocarbon species,
including benzene (C₆H₆), diacetylene (C₄H₂),
and propyne (C₃H₄).

It's long been known that such molecules form in Titan's atmosphere when
ultraviolet rays from the Sun cause reactions that break down methane gas, with
the resulting ions recombining into more complex molecules consisting of chains
of carbon atoms. But these substances are relatively heavy and should sink in
Titan's atmosphere -- in other words, Titan's upper atmosphere should be
stratified by mass. "Titan seems to be mixed all the way to the top. The fact
that we saw these molecules at 1200 kilometers is quite surprising." The
detection "bodes well for the mission," Waite said. "At lower altitudes, we
expect to do even better."

Waite has not yet seen signs of the carbon-nitrogen compounds known as "nitriles"
that are also known to form in Titan's atmosphere. These compounds are of
interest to scientists because they are chemical precursors to very interesting
prebiotic compounds such as amino acids. But Waite expects to see those
materials in future, closer flybys with altitudes nearer 950 kilometers (590
miles). "Benzene and acetylene were easy to spot," he explained. But common
nitriles, such as hydrogen cyanide (HCN) have masses more similar to nitrogen or
methane, making them harder to pick out of the INMS results with only one
night's study.

http://www.planetary.org/news/2004/cassini...28.html