Detection of hydrated, cluster and molecular ions in laboratiry plasma analogous to ionospheric D-region
Abstract
An experiment was conducted to generate and detect hydrated, cluster and molecular ions in conditions close to those in the D- region of the ionosphere. A plasma chamber having a volume of 6.5x103 cm-3 was used to produce nitric oxide plasma with electron density and electron temperatures in the range of 2x103 to 2x104 cm-3 and 1000K to 2000K, respectively using an intense EUV source. After producing the NO+ plasma, controlled amount of water vapor was introduced in to the chamber. Abundance of positive ions produced inside the chamber was measured by a differentially pumped ion quadrupole mass spectrometer, with typical sweep duration of 120 seconds for scanning ion masses from 15 to 135 amu. A Langmuir probe was used to measure the electron density and electron temperature. The ratio of pressure of NO to water vapor was varied from 0.2 to 2.0. A large number of ions, some of which are believed to be produced in such reactions but could not be observed earlier, and some which were not predicted earlier, were observed, in addition to the ions which have been observed before in similar experiments. Mass number of the most dominant ions, which have been detected for the first time, are in order of their abundance 102+, 131+, 115+, 112+, 117+ and 88+. Mass numbers of detected ions with intermediate abundance are: 43+, 83+, 93+, 95+, 99+, 100+, 103+ and with low abundance are: 29+, 54+, 77+, 81+, 107+, 109+, 113+, 114+, 116+, 119+, 123+, 127+ and 128+. All the ions detected in these experiments appear to belong to either of the following categories: (a) hydrated ions of NO+(H2O)n series, NO+(H2O)nX series, NO2+(H2O)n series, O2(H2O)n series, (b) proton hydrates of H3O+(H2O)n series, H3O+(H2O)nX series, H3O+NO(H2O)n series, (c) cluster ions and (d) molecular ions. It was also found that at a given pressure, different ions take different time to come to their peak abundance and this time appears to be pressure dependent. For NO and water vapor pressure of 5x10-2 Torr each, ions with mass numbers 66+, 73+ and 84+ achieved their peak abundance in about a minute, mass numbers 48+, 55+, 83+, 109+ and 131+ in 5 to 10 minutes, mass numbers 91+ and 102+ in 10 to 20 minutes and mass numbers 43+, 88+ and 117+ took more than 20 minutes.
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35..889S