VUV OPTICAL-ABSORPTION AND ELECTRON-ENERGY-LOSS SPECTROSCOPY OF FORMAMIDE

Absolute absorption cross-sections for formamide have been measured us ing a synchrotron radiation source (5-11.2 eV; 250-110 nm), along with electron-energy-loss (EEL) spectra at (i) high incident electron ener gies and low scattering angles and (ii) near-threshold incident energi es and large scattering angles. Tn the optical- and high-energy EEL da ta, the excitation energies of the historical amide absorption bands ( W, R-1, V-1, R-2 and Q) are in agreement with expectation. Vibrational structure is assigned to the V-1 ((1) pi pi) band, It is proposed th at the Q band (similar to 9.2 eV) arises from superposition of transit ions to several Rydberg states, with the second (1) pi pi State (V-2, once related to the Q band) lying at a higher energy; the V-2 state m ay be visible in the EEL data. A number of Rydberg series converging t o the lowest ionisation potential are suggested and the possibility of using these Rydberg data to assign the two first (closely spaced) ion isation potentials is discussed. The near-threshold EEL data fail to r esolve the low-lying (3) pi pi state (the V-1 state triplet) because of spectral congestion. Dissociative electron attachment occurs in for mamide upon impact with electrons of energy around 6.3 eV. (C) 1997 El sevier Science B.V.