Data Set Overview : Mass spectrometric measurements of ions in the coma of comet Giacobini- Zinner were made during the encounter of the International Cometary Explorer (ICE) on 11 September 1985, when the spacecraft passed within 7800 km of the nucleus on its antisunward side. For mass-to-charge (M/Q) ratios from 14 to 33 amu/e-, H20+ was the dominant ion; several other species were also detected.  The ICI was designed for solar wind measurements and was used to study the composition of the solar wind and the velocity distributions of and velocity differences among solar wind ions. The ions in the solar wind are highly charged since they retain the charge states acquired in the corona; the appropriate range of values of M/Q normally covered by the ICI was 1.4 to 5.8 amu/e- measured over a solar wind velocitv (V) range of 300 to 620 km per sec. The ranges of M/Q and V in which observations were made were set by parameters read into the instrument microprocessor through the spacecraft command system. To cover values of M/Q and V appropriate to the comet (where singly charged ions are expected), a set of parameters was found that selected 14 M/Q values between 14 and 33 amu/e- for V between 80 to 224 km per sec and 14 M/Q values between 1.4 and 3 amu/e- for V between 237 and 463 km per sec. The M/Q resolution was in the range 20 to 30 for solar wind observations but depended on the parameter MV/Q and was 11 at M/Q of 33 amu/e- and V of 230 km per sec. During the encounter the spacecraft was moving at a speed relative to the comet of 21 km per sec and crossed its tail almost perpendicularly. The distances travelled by the spacecraft during each measurement were several times the ionic gyroradius in most conditions along the trajectory. Detections were recorded on September 11 from 10:26 through 11:35 UT; closest approach is recorded as 11:02 UT.   Data : Ion Composition Instrument during the International Cometary Explorer encounter:  Arrays are composed of scans in velocity as the M/Q values is held constant. For low mode, there are 14 scans beginning at 1.38 amu/e- and there are 12 velocity steps (unequal) for each M/Q scan. The steps are listed as follows: 237.71 km/s, 252.61 km/s, 268.31 km/s, 285.11 km/s, 302.91 km/s, 321.71 km/s, 341.81 km/s, 363.11 km/s, 385.81 km/s, 409.91 km/s, 435.41 km/s, 462.61 km/s. The process is repeated for 13 additional scans (total of 14) in the following order: 1.38 amu/e-, 1.48 amu/e-, 1.58 amu/e-, 1.67 amu/e-, 1.76 amu/e-, 1.88 amu/e-, 2.00 amu/e-, 2.21 amu/e-, 2.26 amu/e-, 2.40 amu/e-, 2.54 amu/e-, 2.70 amu/e-, 2.87 amu/e-, 3.05 amu/e-. Counts for a 'M/Q vs V' bin are collected every 2.97 seconds, which is one spacecraft spin; there are 420 spins in a complete cycle which spans 21.13 min. The time spent on each scan is 35.72 seconds. The sequence of scans is not continuous but interleaved with the other mode of sampling (M/Q 14-32 amu/e- for V:80-224 km/s); a scan begins every 89.3 seconds in each mode.  For the high mode, there are 14 scans beginning at 14.4amu/e- and there are 18 velocity steps (unequal) for each M/Q scan. The velocity steps are as follows: 80.01 km/s, 85.01 km/s, 90.31 km/s, 95.91 km/s, 101.91 km/s, 108.31 km/s, 115.01 km/s, 122.21 km/s, 129.81 km/s, 137.91 km/s, 146.51 km/s, 155.71 km/s, 165.41 km/s, 175.71 km/s, 186.61 km/s, 198.31 km/s, 210.61 km/s, 223.81 km/s. The process is repeated for 13 additional scans (total of 14) in the following order: 14.4 amu/e-, 15.3 amu/e-, 16.3 amu/e-, 17.3 amu/e-, 18.4 amu/e-, 19.5 amu/e-, 20.8 amu/e-, 22.1 amu/e-, 23.4 amu/e-, 24.9 amu/e-, 26.5 amu/e-, 28.1 amu/e-, 29.9 amu/e-, 31.7 amu/e-. Counts per each M/Q-vs-V bin are collected every 2.97 seconds which is one complete spacecraft spin; there are 420 spins in a complete cycle that takes 21.13 min. The time spent on each scan is 53.58 seconds. The sequence of scans is not continuous but interleaved with the other mode of sampling (M/Q 1.38-3.05 amu/e- for V:237-463 km/s). In each array, a value of -1 indicates no data value.

Review : PDS Peer review was held in Fall 1998.  Data gaps : The original data was submitted as hard copy. The individual arrays were scanned by Image-Right under contract with NSSDC. The period of the hard copy covered from Sept 9 through Sept 13 but it was determined after discussions with the PI (Coplan) that the scans from Sept 11 19:56 through Sept 13 5:41 were suspect (Coplan et al. 1987) so they were not digitized. Only encounter tables are included here.