Hexamethyldisiloxane is used as a silicon-source gas for plasma enhanced chemical vapor deposition (PECVD) growth of silicon oxide films for passivation layers in microelectronics. In order to produce low permeability films, it is necessary to minimize the carbon content. Films were deposited by a mom temperature PECVD process in a parallel plate reactor, and were characterized by infrared spectroscopy, ellipsometry, microbalance, and elastic recoil detection (ERD). The infrared-active carbon groups appear in Si-CH3, CH(x), C=O, and SiC bands. A double band at 2343 cm-1 has also been seen to track these bands. Deposition rate data shows linear behavior as a function of the Hexamethyldisiloxane (HMDSO) concentration in the reactor. The carbon within the films ranges from 36% to < 1 % of the amount of carbon assisted with HMDSO required to grow the films, depending upon the oxygen flow rate. By comparing the ERD composition data to the infrared spectral data, a carbon content correlation value has been found, and a detailed study of the data reveals evidence of C-C bond existence within films having the greatest total carbon content. Finally, it appears that the 2343 cm-1 band corresponds to CO2 rotational bands, in which the distribution of rotational states is evidence of hindered molecular motion.