Of the C _ { 3 } H _ { x } hydrocarbons , propane ( C { { } _ { 3 } } H _ { 8 } ) and propyne ( methylacetylene , CH _ { 3 } C _ { 2 } H ) were first detected in Titan ’ s atmosphere during the Voyager 1 flyby in 1980 .
Propene ( propylene , C _ { 3 } H _ { 6 } ) was first detected in 2013 with data from the Composite InfraRed Spectrometer ( CIRS ) instrument on Cassini .
We present the first measured abundance profiles of propene on Titan from radiative transfer modeling , and compare our measurements to predictions derived from several photochemical models .
Near the equator , propene is observed to have a peak abundance of 10 ppbv at a pressure of 0.2 mbar .
Several photochemical models predict the amount at this pressure to be in the range 0.3 - 1 ppbv and also show a local minimum near 0.2 mbar which we do not see in our measurements .
We also see that propene follows a different latitudinal trend than the other C _ { 3 } molecules .
While propane and propyne concentrate near the winter pole , transported via a global convective cell , propene is most abundant above the equator .
We retrieve vertical abundances profiles between 125 km and 375 km for these gases for latitude averages between 60 ^ { \circ } S to 20 ^ { \circ } S , 20 ^ { \circ } S to 20 ^ { \circ } N , and 20 ^ { \circ } N to 60 ^ { \circ } N over two time periods , 2004 through 2009 representing Titan ’ s atmosphere before the 2009 equinox , and 2012 through 2015 representing time after the equinox .

Additionally , using newly corrected line data , we determined an updated upper limit for allene ( propadiene , CH _ { 2 } CCH _ { 2 } , the isomer of propyne ) .
We claim a 3- \sigma upper limit mixing ratio of 2.5 \times 10 ^ { -9 } within 30 ^ { \circ } of the equator .
The measurements we present will further constrain photochemical models by refining reaction rates and the transport of these gases throughout Titan ’ s atmosphere .