Electron transmission spectroscopy is used to study shape resonances (temporary negative ions) in benzene and some isolectronic N−heterocyclic molecules (pyridine, diazines, and s−triazine), in the energy range 0−6 eV. The lowest shape resonance in each of these molecules exhibits vibrational structure which is interpreted in all cases as the totally symmetric C−C stretch mode. The ground vibrational level of this lowest shape resonance is accessible by electron impact only in benzene and pyridine. Thus, their electron affinities can be determined from the present experiment (−1.15 eV for C6D6 and −0.62 eV for C5H5N). Only excited vibrational levels are accessible in the diazines and s−triazine, indicating that the electron affinities for these molecules have positive values. For benzene, pyridine, and some other aromatic hydrocarbons, we compare the electron affinities established in the gas phase with the polarographic potentials established in the liquid phase and we find a linear relationship. Using this correlation in conjunction with the measured values of the polarographic potentials, we estimate the electron affinities for pyridazine (0.25 eV), pyrimidine (0 eV), pyrazine (0.40 eV) and s−triazine (0.45 eV).

Poly(ether-sulfone)s having an identical backbone were prepared by four different methods. First, silylated bisphenol A (BSBA) was polycondensed with 4,4′-difluorodiphenyl sulfone (DFDPS) and K 2CO3 in N-methylpyrrolidone with variation of the temperature. Second, analogous polycondensation were conducted using CsF as catalyst (and no K2CO3). Third, CsF-catalyzed polycondensations BSBA and DFDPS were conducted in bulk up to 290°C. Fourth, free bisphenol was polycondensed with DFDPS or 4,4′-dichlorodiphenyl sulfone and K2CO3 in DMSO with azeotropic removal of water. MALDI-TOF mass spectroscopy revealed that the first method mainly yielded cyclic poly(ether-sulfone)s which were detected up to masses around 13 000 Da. These and other results suggest that these polycondensations take a kinetically kontrolled course at tempeatures e145°C. This interpretation is also valid for the fourth method where high yields of cycles were obtained with DFDPS. With the less reactive 4,4′-dichlorodiphenyl sulfone lower conversions, lower molecular weights and lower fractions of cycles were found. In contrast to KF (resulting from K 2CO3) CsF cleaves the poly(ether sulfone) backbone at temperatures > 145°C. Smaller amounts of smaller cycles were found in these CsF-catalyzed polycondensations which were in this case the result of thermodynamically controlled "back-biting degradation".

Compound states of triatomic molecules and simple hydrocarbons are studied using electron transmission spectroscopy. Structures in the derivative of the current transmitted through a gas-filled collision chamber are interpreted as resonances in the electron-molecule cross sections. At low electron energies (0–6 eV) we observe, in N2O, H2S, and C2H4, broad and featureless structures which we identify as shape resonances. In the same energy range, the molecules CO2, NO2, C6H6, and SO2 exhibit narrow structures which form vibrational progressions. In CO2, NO2, and C6H6, these vibrational progressions are identified as shape resonances; in SO2, the interpretation is not clear cut. No low-energy resonances are observed in H2O and in CH4. At higher energies (9–17 eV) we observe sharp structures for H2O, H2S, N2O, CO2, and C2H4 (but not for C6H6 and CH4). These structures form bands, each band consisting of a vibrational progression. The states which are responsible for the bands consist of two Rydberg electrons moving in the field of a particular positive-ion core. These bands are similar to those found previously in diatomic molecules.

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