V. A. Mazunov

RESONANT ELECTRON CAPTURE MASS SPECTRA OF FULLERENES C60 AND C70

Resonant electron capture by C60 and C70 was studied and it was established that long-lived (i.e. mass spectrometrically observable) parent negative ions are formed within an extremely broad energy region (0–14 eV). It has been shown that effective yield curves of C60− and C70− in the thermal energy region have resonant peaks at 0.05 ± 0.01 and 0.06 ± 0.01 eV, respectively. Owing to the higher energy resolution than in previously published experiments, it was possible to observe another resonant state at ca. 0 eV for both fullerenes (as a shoulder on the effective yield curve). This gives evidence of the possibility of s-electron attachment by the fullerenes. A correlation between electron capture, electron loss energy and photoelectron spectra was found. At 6.5 eV and above, C60− and C70− are subject to electron autodetachment and mean lifetime and mean decay rates were directly measured.

Resonant free electron capture spectra of C60F48

Abstract Resonant electron capture spectra of C 60 F 48 and its oxy-analogue C 60 F 48 O have been studied and interpreted. Long-lived parent negative ions are formed within a 0–8 eV energy range with a maximum yield at approximately 0.14 eV. Going from thermal energy and up to 8 eV, these parent anions undergo fragmentation with generation of even-numbered fluorine negative ions due to sequential loss of F 2 down to C 60 F 36 − and C 60 F 36 O − , respectively; the yield of fragment anions at thermal energy rises with the degree of fragmentation. At approximately 8 eV and above, the odd-numbered fluorine fragment anions were registered. The formation of these anions in the energy range 17–45 eV was associated with the resonant state where the excitation of σ-plasmons is supposed to occur. The appearance energies of positive parent and fragment ions from C 60 F 48 as well as parent C 60 F 36 + have been measured. The parent ion C 60 F 48 − undergoes electron autodetachment at 3–4 eV with a mean lifetime in the millisecond scale. Estimations for CF bond dissociation energy and electron affinity of C 60 F 47 are reported. Published by Elsevier Science B.V.

Thermochemistry of negatively charged ions. II. Energetics of formation of negative ions from acridanone and some of its derivatives

Dissociative electron capture mass spectra in the range 0–10 eV were registered for the antiviral drugs acridanone and acridanoneacetic acid and its n-hexyl and benzyl esters. The appearance energies (AEs) of fragment negative ions from these and some model compounds (carbazole, acetic acid) were measured. The following thermochemical data were deduced from experiment: electron affinities (EAs) 2.44, 3.08 and 4.12 eV for carbazolyd, 8-oxyacridane and acridanone-N-methyleneacetoxy free radicals, respectively, and ΔHacid values 324.5 and 320.7 kcal·mol−1 for acridanoneacetic and 8-hydroxyacridane, respectively. The data for CH3COOH were: ΔHacid (CH3COOH) = 343 ± 1 kcal·mol−1 and EA(CH3COO·) = 3.31 ± 0.05 eV. Intense formation of RCOO− carboxylate ion from acetic acid, acridanoneacetic acid and its benzyl ester contrasted with the as yet unexplainable absence of this ion in the mass spectra of CH3COOEt and of the n-hexyl ester of acridanoneacetic acid. It was demonstrated that the [M−H]−1 ion from acridanone possesses the structure of acridane-8-oxy anion rather than N-centred acridanonide anion. The appearance of some fragment ions at unexpectedly low AEs (≤0) was explained by their formation from free radicals produced thermocatalytically in the instrument. The estimation schemes for the enthalpies of formation of more than 20 free radicals and anions, based on the earlier established regularities,1,, 2 are described in detail. Some of the data for known species were revised: ΔH0f (HCCO·) and ΔHacid (HCCOH) 48.5 and 350 kcal·mol−1 (compare with 42.4 and 365 in Ref. 3) or EA C4H4N· (pyrrolide) 1.53 eV (2.4 eV, Ref. 3) Copyright

Mechanism of negative ion formation from phenol and para‐chlorophenol by interaction with free electrons

Dissociative electron attachment (DEA) to phenol and para-chlorophenol in the energy range 0-12 eV is studied. Analogies in formation of the resonance states in an ionic benzene and its derivatives are found to arise from the similarity of the aromatic base of the molecules. Differences in DEA processes are defined mainly by the influence of the functional OH-group and, to a lesser degree, by the presence of a chlorine atom. A correlation between the energies of the resonance states and ionization energies of p-chlorophenol and phenol, analogous to that found previously for phenol, is proved. On this basis it is established that the dominating mechanism for formation of molecular negative ions at energies above 5 eV is Feshbach resonance.Copyright 2000 John Wiley & Sons, Ltd.

Thermochemical determination of the structure of negative ions on the basis of data from resonance electron capture mass spectrometry. Phenol, its chlorinated derivatives and a thioanalogue

Appearance energies for [M - H](-) ions from phenol (I), 4-chlorophenol (II), pentachlorophenol (III) and pentachlorothiophenol (IV) were measured. The following thermochemical data were deduced from experiment: DeltaH(acid) values of 343.3, 335.7, 317.1 and 317.1 kcal mol(-1) for RH molecules (I, II, III, and IV, respectively) and electron affinities (EAs) of R(.) free radicals 2.55, 2.90, 3.79, and 3.65 eV, respectively. Our data for phenol (I) and 4-chlorophenol (II) demonstrate a higher stabilization of ArO(-) anions than was previously accepted. Using the enthalpic shift procedure for molecules and a series of isodesmic reactions for free radicals, earlier elaborated by the authors, a new Delta

Thermochemical determination of the structure of negative ions with the data from resonance electron capture spectrometry. 2. 5-Substituted 2-furancarboxylic acids and their esters

bf H_bf fbf 0

THE ENERGETICS OF RESONANT DISSOCIATIVE ELECTRON ATTACHMENT TO MOLECULES OF FIVE-MEMBERED HETEROCYCLIC COMPOUNDS

values for the following gas-phase species were obtained (kcal mol(-1)): C(6)Cl(5)Br (5.0), C(6)Cl(5)SH (8.5), p-ClC(6)H(4)C(.) (2. 0), C(6)Cl(5)C(.) (-15), C(6)Cl(5)S(.) (44). Copyright 2000 John Wiley & Sons, Ltd.

Specific features of resonance electron capture mass spectra of ecdysteroid molecules

The energetics of isomerization and fragmentation of carboxylic acids and their esters from the furan series were investigated in conditions of resonance electron capture with the formation of negative ions. The enthalpies of formation of fragmentary negative ions were determined and the structure of some charged and neutral products of dissociation of these compounds was established. Schemes of the hydrogen and backbone rearrangements were proposed.

Processes of dissociative electron capture by 20-hydroxyecdysone molecules

The thermochemistry of resonant dissociative electron attachment processes for furan, thiophene, selenophene, and pyrrole molecules has been studied. The structures of the dissociation products originating from negative molecular ions at energies ranging from 2 to 6 eV have been established using the measured appearance energies of fragment ions and the known thermodynamic functions of radical and molecular dissociation products. Heats of formation and electron affinities for some radicals and molecules have been assessed by calculations and estimated experimentally. It has been concluded that the majority of the fragment ions are formedvia rearrangement processes in molecular or fragment ions.

Phenol, chlorobenzene and chlorophenol isomers: resonant states and dissociative electron attachment

Specificity of the dissociative attachment of low-energy electrons to ecdysteroid molecules (viz., 20-hydroxyecdysone 2,3:20,22-diacetonide, 20-hydroxyecdysone 20,22-acetonide, and poststerone 2-acetate) was found, which is manifested as the formation of long-lived pseudo-molecular negative ions that appeared due to the elimination of the H2 and H2O molecules. These rearrangements are resulted from the formation of the system of conjugated double bonds in the ecdysteroid skeleton, stabilizing the lowest vacant molecular orbital.