OBSERVATION OF AN ELECTRONICALLY EXCITED-STATE OF H-3 AND DETERMINATION OF ITS VIBRATIONAL LEVEL STRUCTURE

Discrete energy levels of H3 are observed by measuring the translational-energy spectrum of H-H2 fragment pairs arising from predissociation of H3. The translational-energy spectrum exhibits structure in the range from 3.5 to about 6 eV. The excited H3 molecules are obtained in electron-capture collisions of 10-keV H3+ ions on H2. The H3+ ions are produced in an electron-impact ion source at high hydrogen pressure. The translational-energy spectrum of H-H2 fragment pairs is measured with a flight-time-difference method. The energies and intensities of the observed peaks are compared with calculations by Porter. The observed levels can be attributed to vibrational levels in the upper Jahn-Teller sheet of H3. The spectrum can be described very well using the following parameters: The ground vibrational level in the upper Jahn-Teller sheet lies at 3.50 eV above H+H2 in its ground vibrational level. The vibrational quanta are 0.32 and 0.49 eV for the breathing and degenerate vibrations, respectively. © 1979 The American Physical Society.