Chemistry of protoplanetary disks have focused on the inner (R<5AU) or outer disk (R>100 AU) but not in the 5-30 AU region where giant planets are formed. The hot organic chemistry of 5-30 AU region can be explored with Herschel. We tentatively detected CH+ emission in four disks at 72.14 micron. CH+ is a starting ion in the reaction network leading to methane, HCN, of C2H2. Two of the disks are known to have an inner gap up to ~10AU. We propose to obtain deep observations of three rotational transitions of CH+ with Herschel-PACS. The aims of the proposals are: 1) confirm the detections, 2) study the excitation condistions of CH+ in disks, 3) explore the hot carbon chemistry in disks with our chemical code, 4) understand the role of inner gap in the disk chemistry.
Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.