title: Upper limits for undetected trace species in the stratosphere of Titan.
abstract: In this paper we describe the first quantitative search for several molecules in Titan's stratosphere in Cassini CIRS infrared spectra. These are: ammonia (NH3), methanol (CH3OH), formaldehyde (H2CO), and acetonitrile (CH3CN), all of which are predicted by photochemical models but only the last of which has been observed, and not in the infrared. We find non-detections in all cases, but derive upper limits on the abundances from low-noise observations at 25 degrees S and 75 degrees N. Comparing these constraints to model predictions, we conclude that CIRS is highly unlikely to see NH3 or CH3OH emissions. However, CH3CN and H2CO are closer to CIRS detectability, and we suggest ways in which the sensitivity threshold may be lowered towards this goal.
authors.affiliation: Department of Astronomy, University of Maryland, College Park, MD 20742, USA. conor.a.nixon@nasa.gov
authors.forename: Conor A
authors.initials: CA
authors.lastname: Nixon
authors.forename: Richard K
authors.initials: RK
authors.lastname: Achterberg
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Teanby
authors.forename: Patrick G J
authors.initials: PG
authors.lastname: Irwin
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Flaud
authors.forename: Isabelle
authors.initials: I
authors.lastname: Kleiner
authors.forename: Alix
authors.initials: A
authors.lastname: Dehayem-Kamadjeu
authors.forename: Linda R
authors.initials: LR
authors.lastname: Brown
authors.forename: Robert L
authors.initials: RL
authors.lastname: Sams
authors.forename: Bruno
authors.initials: B
authors.lastname: Bézard
authors.forename: Athena
authors.initials: A
authors.lastname: Coustenis
authors.forename: Todd M
authors.initials: TM
authors.lastname: Ansty
authors.forename: Andrei
authors.initials: A
authors.lastname: Mamoutkine
authors.forename: Sandrine
authors.initials: S
authors.lastname: Vinatier
authors.forename: Gordon L
authors.initials: GL
authors.lastname: Bjoraker
authors.forename: Donald E
authors.initials: DE
authors.lastname: Jennings
authors.forename: Paul N
authors.initials: PN
authors.lastname: Romani
authors.forename: F Michael
authors.initials: FM
authors.lastname: Flasar