Imaging of direct photodetachment and autodetachment of (OCS)2-: excited-state dynamics of the covalent dimer anion

We report a photoelectron imaging study of (OCS)-2 and compare the results to OCS-.H2O. Two electron-emission mechanisms are observed for the dimer anion: direct photodetachment and autodetachment, while OCS-.H2O exhibits only the direct mechanism. The results provide evidence of covalent (OCS)-2 coexisting with the OCS-.OCS cluster anion. The autodetachment originating from the covalent species is modeled as thermionic emission transpiring in the regime of fragmentation. The bulk statistical model is found applicable to the small anion due to the availability of low-lying excited states.     

Stability of the ground state vinylidene anion H2CC-

A technique to measure very low collisionless decay rates of ionic species has been applied at a new electrostatic storage ring to obtain the rate for spontaneous rearrangement of the vinylidene anion to neutral acetylene. The measurement yields a rate of k(0) = (0.009+/-0.006) s(-1), corresponding to a natural lifetime of the vinylidene anion of tau(0) approximately 110 s.     

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.     

Free energy barrier for dissociation of the guanosine monophosphate anion in water

We report free energy barriers for the ground-state dissociation of the guanosinenucleotide anion in solution, employing implicit and explicit solvation models. The latterwas based on the Free Energy Perturbation technique and Monte Carlo simulations. For thelowest-energy structure, both solvation models indicate a solvent-induced transition froma dipole-bound state in the gas phase to a π^? valence state in solution. The freebarrier estimates obtained from explicit and implicit solvation are in fair agreement witheach other, although significantly overestimated in comparison to a previously reportedexplicit solvation model based on ab initio molecular dynamics simulations. Accounting forcorrections related to the different DFT functionals used in the present and previousstudies significantly improves the agreement.     

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.     

Application of the united atom model for estimating the lifetime of negative molecular ions relative to electron autodetachment

A model proposed for describing the scattering of low-energy electrons (whose energy ranges between thermal energy and several electronvolts) from polyatomic molecules makes it possible to estimate the lifetime of shape resonances. The parameters of the model are determined by specific structural and experimental characteristics of molecules. The results of approximate computations of the lifetimes for negative ions of molecules with different symmetries (diatomic halogens, parabenzoquinone, fullerene C₆₀, benzothiadiazoles, anthraquinone derivatives, and substituted benzene forms) are presented. The obtained data show that the lifetimes are sufficient for the formation of fragment ions observed in the mass spectra of negative ions.     

Lowest excited states of 2-aminopurine

Absorption and fluorescene spectra and quantum yields of emission over a wide range of pH and solvent polarity were measured for 2-aminopurine and 2-dimethylaminopurine. An increase in dipole moment and a rise of pK values for N₁(N₃) ring atom protonation in the excited state were demonstrated. Thus, the lowest excited singlet state shows partially the (1, a_π¹) configuration. The polarization, lifetimes and the phosphorescence-to-fluorescence ratios indicate that spin-orbit coupling of ¹(n, π¹) and ¹(1, a_π¹) with the lowest triplet state is the main source of phosphorescence intensity. The matrix element of spin-orbit coupling of ¹(n, π¹) to the T₁ state is about 33 times larger than that of ¹(1, a_π¹). The temperature- dependent process of 2-aminopurine fluorescence quenching in either is presumably due to the thermal population of the second excited triplets state of (n, π¹) configuration, which can approximately be located at 370 cm^-1 above the lowest (1, a_π¹) singlet.     

Lowest excitation energy of 9Be

Variational calculations employing explicitly correlated Gaussian functions and explicitly including the nuclear motion [i.e., without assuming the Born-Oppenheimer (BO) approximation] have been performed to determine the lowest singlet transition energy in the 9Be atom. The non-BO wave functions were used to calculate the alpha2 relativistic corrections (alpha=1/137.035,999,679). With those corrections and with the alpha3 and alpha4 QED corrections determined previously by others, we obtained 54,677.35 cm(-1) for the 3(1)S-->2(1)S transition energy. This result falls within the error bracket for the experimental transition of 54,677.26(10) cm(-1). This is the first time an electronic transition of Be has been calculated from first principles with the experimental accuracy.     

Lowest energy Cooper pairing in the presence of antiferromagnetism

Cooper pairing of electron eigenstates of an antiferromagnet involves considerable complexity in spin space and in phases of the order parameters. With a BCS interaction the pairing scheme with lowest free energy has anisotropic spin-matrix order parameter $\textcolor{red}{}\text{(}\text{k}\text{); however}\textcolor{red}{}{}^{\mathrm{+}}\text{(}\text{k}\text{)}\textcolor{red}{}\text{(}\text{k}\text{)=|△|}{}^2\textcolor{red}{}$. Magnitude of the anisotropic order parameter satisfies the simple BCS gap equation but with electron energies of the antiferromagnet eigenstates appearing instead of Bloch state energies of the nonmagnetic crystal.     

Lowest breathing mode of bosonic helium clusters

We analyze various microscopic calculations of vibrational frequencies for ⁴He_N clusters, N = 3-728. The lowest breathing frequency with total angular momentum J = 0 varies smoothly as a function of N, with a maximum around N = 50-120. Received 11 July 2001     

Extraction of selected incapacitating agents by bis-1,2-dicarbollylcobaltate anion from water into chloroform

Bis-1,2-dicarbollylcobaltate anion, labelled by ⁶⁰Co, forms ionic associates with cations of some incapacitating agents. Their stability and partition between aqueous 0.1 mol.L⁻¹ HCl and chloroform were investigated radiometrically. A method of competitive extraction was proposed for some anions of dyes which were so far used for extraction-spectrophotometric determination of some agents.     

On the Origin of the Lowest Excited Singlet State in Retinyl Acetate

Abstract

Employing the techniques of a circular dichroism (CD) and a fluorescence polarization (FP), the long-wavelength forbidden ¹A^?- _g → ¹A^? _g transition in the absorption spectrum of retinyl acetate at 293K has been found. The FP degree of retinyl acetate in cyclohexanol decreases from 0.28 at 330 nm (the area of a strongly allowed ¹B?_u → ¹A^? _g transition) to 0.21 at 360 nm (the area of forbidden ¹A^?- _g → ¹A^? _g transition).     

Scaled equation of state for supercooled water near the liquid-liquid critical point

We have developed a scaled parametric equation of state to describe and predict thermodynamic properties of supercooled water. The equation of state, built on the growing evidence that the critical point of supercooled liquid-liquid water separation exists, is universal in terms of theoretical scaling fields and is shown to belong to the Ising-model class of universality. The theoretical scaling fields are postulated to be analytical combinations of the physical fields, pressure, and temperature. The equation of state enables us to accurately locate the "Widom line" (the locus of stability minima) and determine that the critical pressure is considerably lower than predicted by computer simulations.     

One-dimensional approximation of the effective rotational Hamiltonian of the ground state of the water molecule

A method is presented for summation of the divergent perturbation-theory series used in molecular spectroscopy, by means of a one-dimensional approximation. Application of the proposed method enables one to fit the energy levels of the ground state of the water molecule (Mol. Phys. 32, 499–521 (1976)) to a maximum difference between the observed and the calculated levels of less than 8 cm^?1 for levels with the maximum rotational quantum numbers K = 20 and J = 20 in a model with 24 parameters and terms up to J⁸.     

An NMR relaxation study of the state of water in gelatin gels.

A combination of 1H and 23Na NMR is used to probe the dynamic state of water in gelatine gels as the water content is lowered from 70% to dryness. A sharp increase in the proton and sodium transverse relaxation rates is observed as the water content falls from 20 to 15% while the proton longitudinal and dipolar cross relaxation rates show a maximum at ca. 15%. We show that these observations can be understood if monolayer coverage occurs at 15% and multilayers of less strongly interacting hydration water are formed between 15 and 20%. Above 20% the water appears to behave as an unperturbed bulk phase.