Hidden rearrangement processes in short-lived negative molecular ions

The study of resonant electron capture by nitrobenzene molecules showed that some fragmentary negative ions are unstable toward electron autodetachment. The measured appearance energy of the neutral component of an [M — H]⁻ ion beam does not agree with the energetics of direct dissociation in a molecular ion. The estimation calculations show that the low appearance energy of [M — H]⁰ neutral components is caused by isomerization of a molecular ion of nitrobenzene to the 2-nitrobenzene structure followed by the formation of a phenoxide ion in the autodetachment state. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 367–370, February, 2006.     

Resonant electron capture by uridine

Processes of the resonant electron attachment to uridine molecules have been studied in the energy range 0–14 eV. The main fragmentation channels of negative molecular ions have been determined. Long-lived negative molecular ions have been detected in the thermal energy region. It was found that these ions form in a dipole-bound state. The lifetime of molecular ions was estimated at τ_a ～ 29 × 10^?6 s.     

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.     

Complex compounds based on a colchicine derivative

Complex compounds based on deacetyl-10-ethanolamino-10-demethoxycolchicine with Co, Mn, and Fe chlorides have been obtained, and their radiomodifying and antitumoral properties have been investigated.Tashkent State University, 700095, Tashkent, CIS, Vuzgorodok. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 728–730, September–October, 1996. Original article submitted November 5, 1994; revision submitted April 7, 1995.     

Dissociative electron attachment to glycyl-glycine, glycyl-alanine and alanyl-alanine

The processes of negative ions formation of dipeptides glycyl-glycine, glycyl-alanine and alanyl-alanine in the conditions of resonant electron capture have been studied with a help of negative ions mass spectrometry. Using a thermochemical approach, the main channels of fragment negative ions formation were found and the structure of the ions were established. The isobaric ions have been identified by the experiments with high mass resolution. The cross sections of fragment ions formation were measured. The metastable fragmentation of [M-H](-) and [M-COOH](-) ions in the energy range 4.5-7.5 eV have been found.     

Formation of doubly charged negative ions under the conditions of the resonant electron capture by fluorofullerenes

Doubly charged negative ions formed when electrons with controlled energies interact with isolated fluorinated fullerene molecules C₆₀F _n (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 C₆₀F ₃₆ ^2? and C₆₀F ₄₈ ^2? 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.     

Local canted spin behaviour in Co1.4−x Zn x Ge0.4Fe1.2O4 spinels: A macroscopic, mesoscopic and microscopic study

DC magnetization, neutron depolarization and neutron diffraction (with both polarized and unpolarized neutrons) measurements have been reported for the Co_1.1−x Zn _x Ge_0.1Fe_1.2O₁ spinels with x=0.5, 0.6 and 0.7. Neutron depolarization and neutron diffraction measurements confirm the presence of a long range ferrimagnetic ordering of the local canted spins in these ferrite samples. The observed features of low field magnetization have been explained under the framework of thermally activated domain wall movement of ferrimagnetic arrangement of local canted spins. An important role of magnetic anisotropy (due to the presence of Co²⁺ ions) in establishing the magnetic ordering and domain kinetics in these ferrites has been observed.