R. V. Khatymov

Specific formation of (M-H)− ions from OH-group-containing molecules

Abstract The formation of (M-H) − ions from OH-containing benzene derivatives, covering azobenzenes and phenols, has been investigated by resonant electron-capture mass spectrometry. A vibrational fine structure in the effective ion yield curves, at threshold energies for the formation of these ions through OH-bond cleavage, has been observed. This vibrational progression has been assigned to the ν(OH) stretching mode. It has been supposed that the formation of these ions occurs by a predissociation of the vibrationally excited ground state of the parent anion.

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

Lifetime of negative molecular ions of tetracene and pentacene with respect to the autodetachment of an electron

The processes of nondissociative resonant attachment and autodetachment of electrons in a number of poly-cyclic aromatic hydrocarbon molecules have been investigated by mass spectrometry. Long-lived negative molecular ions of phenanthrene and triphenylene have not been observed. Such ions have been detected for anthracene, pyrene, and benzo[e]pyrene capturing thermal electrons. Negative molecular ions of tetracene and pentacene have also been observed up to 2.5–3 eV. The lifetimes of these ions with respect to the auto-detachment of an electron have been measured throughout the energy range where they are observed. This lifetime for tetracene and pentacene is more than 10 ms, which is two or three orders of magnitude larger than that for remaining compounds. Correlation between the lifetime of ions and the electron affinity of the molecules has been revealed.

Slow decay of negative molecular fluorofullerene ions in the electron autodetachment process

The mean lifetimes of negative molecular ions of C60 fullerene and its fluoroderivatives C60F18 and C60F36 with respect to the autodetachment of electrons have been measured as functions of the ionizing electron energy by the method of mass spectrometry of electron resonance capture. The lifetimes of negative ions in the compounds under investigation are within the one-second range, and an increase in the number of addends leads to an increase in the lifetimes of negative ions by 1.5–2.5 orders of magnitude.

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

Processes of hydrogenation of trifluoromethylfullerenes in the mass spectrometer ion source

bf H_bf fbf 0

Formation of Doubly Charged Negative Ions under the Conditions of the Resonant Electron Capture by Fluorofullerenes

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.

The fragmentation of negative ions of fullerene C60 trifluoromethyl derivatives

The processes of hydrogenation of a mixture of trifluoromethylfullerenes was studied in situ by means of positive-and negative-ion mass spectrometry. The effective addition of 1, 5, and 11 hydrogen atoms was revealed. The appearance energies of positive trifluoromethylfullerene ions C60 (CF3)n+ (n = 1–8) and C60(CF3)nH+ (n = 1, 3, 5, 7) were determined.

Specific features of resonance electron capture mass spectra of ecdysteroid molecules

Doubly charged negative ions formed when electrons with controlled energies interact with isolated fluorinated fullerene molecules C60Fn (n = 36, 48) have been detected and investigated by resonant electron capture mass spectrometry. The dependence of the intensity of the formation of doubly charged negative ions of fluorofullerenes on the energy of attached electrons has been measured. An original method, which is based on the experimental data and does not require additional calibration quantities, has been developed for estimating the absolute cross section for the formation of doubly charged negative ions. The absolute cross sections for the formation of the most intensely formed ions C60F362− and C60F482− are estimated to be about 1.1 × 10−24 and 1.5 × 10−24 m2 at their maximum-yield energies of 2.0 and 1.6 eV, respectively.