ENHANCED FORMATION OF MULTIPLY CHARGED IONS IN NEGATIVE ION FIELD DESORPTION MASS SPECTROMETRY OF ORGANIC COMPOUNDS E. BRAMER-WEGER, S. THIEBES and F.W. RÖLLGEN J. Phys. Colloques, 50 C8 (1989) C8-159-C8-162 DOI: 10.1051/jphyscol:1989828