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1.
The ionization and solution enthalpies of o-methoxybenzoic acid have been measured in H2O-DMSO mixtures. In the same solutions, the ΔG0 values for the ionization process have been determined by potentiometric measurements. A study of the ortho effects by means of a linear combination of the ordinary polar, proximity polar, and steric effects was also performed. The CH3O group seems to undergo a partial steric inhibition of resonance. Finally, the proton transfer process from the ortho derivative to benzoic acid, compared with the same process in the gaseous phase, is presented.  相似文献   

2.
The effect of substituent on the enthalpy ΔH 0 and free energy ΔG 0 of complexation, on the dipole moments of complexes μC and coordination bonds μDA, and on the degree of charge transfer Δq was analyzed for 20 series of complexes with D→A coordination bonds (D = N, O, S; A = B, Al, Ga, Sn, Sb), hydrogen bonds, and charge transfer. It was found that ΔH 0, ΔG 0, μC, μDA, and Δq depend not only on the inductive and resonance effects, but also on the polarization effect of substituents; its contribution varies in a wide range and can exceed 50%.  相似文献   

3.
Infrared—ultraviolet double resonance spectroscopy is used to demonstrate rapid collision-induced V-V transfer between the v6 and v4 vibrational manifolds of D2CO. The rate of transfer is at least gas-kinetic and is explained in terms of Coriolis coupling and rotationally specific, quasi-resonant relaxation channels  相似文献   

4.
The fumaric nitrile-benzene charge transfer complex has been investigated. The equilibrium constant K has been determined by both ultraviolet and nuclear magnetic resonance spectroscopy, following the method of Benesi-Hildebrand. The experimental result kNMR > KUV is associated with the structure of the complex.  相似文献   

5.
6.
In the first Born approximation the dependence of the yields of the1 P and1 D resonances in the He(e, 2e)He+ reaction on the momentum transfer in the recoil peak region at incident energiesE 0=1000 eV is studied. It is shown that in a certain range of the ejection angle and for the large momentum transfer the yield of the1 D resonance dominates over the1 P resonance one.  相似文献   

7.
In this review, the contribution of spin chemistry (in particular, magnetic resonance-related chemistry) to the photochemical field is briefly introduced. First, the development of a time-resolved EPR method and its significant application to radical-related physical phenomena and chemical reactions are presented. Second, a reaction-control method by means of electron spin operations is introduced, and several reaction yield-detected magnetic resonance (RYDMR) methods are presented as applications of this concept. One of the most important physical conclusions is the introduction of the concept of “spin phase relaxation” termed singlet–triplet (ST) and triplet–triplet (TT) dephasing, instead of the traditional concepts of longitudinal (T1) and transversal relaxations (T2). The effects of strong microwave power on the RYDMR spectrum and time-domain data are analyzed according to this concept. Furthermore, a new detection method is introduced, termed “photoconductivity detected magnetic resonance” (PCDMR), which is applicable exclusively to the system of charge transfer reactions.  相似文献   

8.
The cross section for the fine-structure excitation transfer Cs(6P 1/2) → Cs(6P 3/2), induced by collisions with the ground state potassium atoms, has been measured by resonant Doppler-free two-photon spectroscopy. The population densities of caesium 6P J (J=1/2, 3/2) levels were probed by thermionic detection of the collisionally ionized caesium atoms from the Cs(6P J ) → Cs(10S 1/2) excitation channel. The cross section for the transfer process at the temperatureT=503 K has been found to be σ(1/2 → 3/2)=45 Å2 ± 20%. The result is compared with previously published experimental cross sections for fine-structure transfer in resonance states of other alkali elements perturbed by potassium and a thoeretical value of the Li(2P J )-K system calculated in a simple approach.  相似文献   

9.
The absorption and fluorescence spectra of 1-fluorenecarboxylic acid and its anion have indicated that charge transfer interaction between the COOH group and the fluorene ring is more than that of the COO group with the ring, both in the S0 and S1 states. This has been explained by the greater possible resonance interaction between the aromatic ring and the COOH group than with the COO group. The respective interactions between the COOH or the COO group and the fluorene ring in the case of 9-fluorenecarboxylic acid is virtually negligible, both in the S0 and S1 states. The COO group becomes coplanar with the ring when deprotonation takes place at position 9. Various proton transfer reactions have been studied and pKa values in the S0 and S1 states have been determined and discussed. The behaviour of the acids is confirmed by undertaking a similar study with their respective esters.  相似文献   

10.
We have made zero-field optically-detected magnetic resonance measurements on the triplet state of naphthalene-d8 incorporated in the heavy-atom host crystals p-dichlorobenzene, p-dibromobenzene, and s-tetrachlorobenzene. The dependence of the relative triplet sublevel populating rates on the exciting wavelength is interpreted in terms of the electronic excitation transfer mechanisms. We find that upon excitation of the host S1 ← S0 transition in p-dichlorobenzene, energy transfer to the guest T1 takes place via the guest S1, whereas in the other host crystals the intermediate is mainly the host T1 band. Upon host T1 ← S0 excitaton, trapping takes place from a spin-aligned excitor band in s-tetrachlorobenzene, whereas the initial alignment is lost prior to trapping in the dihalobenzene hosts.  相似文献   

11.
The effects are considered of the vibrations occurring with the group of atoms peripheral towards the hydrogen bond on the IR spectrum of the model hydrogen bond. It. is shown that the resonance of the vOHvCH stretching vibrations in a hydrogen bonded molecule result in the division of the vOH band into two other bands having different polarizations. The resonance interaction leads to redistribution of the intensity and perturbs the regular Franck—Condon type envelope of the spectrum.  相似文献   

12.
Cross sections for electron energy transfer from the initial rotational stateJ′of the two lowest vibrational levelsv′=0 andv′=1 of excited dimers Na2(A) to potassium atoms as described by Na2(A1Σ u + ,vJ′)+K(4S)→Na2 (X1Σ g + ,vJ″)+K(4P)+ΔE have been examined by laser-induced fluorescence. A strong increase of the cross section by as much as an order of magnitude has been observed for those dimervJ′-levels for which the dipole transitions are close to resonance of the 4S-4P transitions in the atom (ΔE<4 cm?1). The absolute cross sections for energy transfer have been calculated by the Rabitz approximation of first-order perturbation theory. In the case of closest energy resonance (ΔE=0.9 cm?1) the cross section is Q=7.8×10?13 cm2.  相似文献   

13.
Vacuum ultraviolet radiation is observed through a sampling orifice in a metal cone inserted directly into an Ar inductively coupled plasma (ICP). The many-lined spectrum of the H2 Lyman bands is observed from an argon ICP with either H2 gas or nebulized water added. The most prominent bands are from the ν = 3, 4, 5 or 6 vibrational levels of the B 1Σ+u electronic state of H2. The energies of the ν = 3, 4 and 5 levels are close to those of the Ar metastable levels and of photons from the Ar resonance lines (11.5 to 11.8 eV). These H2 levels are probably populated at least in part by selective energy transfer reactions between Ar metastable atoms and H2 and/or by absorption of Ar resonance photons by H2. The H2 emission emanates only from the upstream reaches of the axial channel, i.e. the part of the axial channel that is inside the load coil and induction region.  相似文献   

14.
We have determined effective cross-sections for resonant transfer of excitation energy from state-selected Li2 molecules to ground state Li atoms $$Li_2 A\left( {\upsilon ',J'} \right) + Li2S \to Li_2 X\left( {\upsilon '',J''} \right) + Li2P$$ with two different experimental techniques. Absolute cross-sections were derived from lifetime measurements of 114 rotational levels of theA-state subject to resonant collisions which belong to vibrational statesv′=4, 5, 6, 7 and 11 of6Li2 and7Li2. Cross-sections amount to several thousand Å2 dropping off sharply with a resonance half-width of about 16 cm?1. The resonance behaviour of the collision cross-section inferred from lifetime data could be confirmed by a double resonance technique probing the number of excited atoms with a second laser while the first laser was scanned over the Li2 X?A absorption band. Due to their high reliability our data prove a good basis for the test of theoretical models. In contrast to earlier investigations significant deviations were found to exist between the measured cross-sections and those predicted by the first-order dipole-dipole scattering theory.  相似文献   

15.
The atomic form factor for the ground state of vanadium is evaluated using non-relativistic and “relativistic-corrected” configuration interaction wavefunctions in the |LSM L M s 〉 representation. Relaxing the constraints imposed by the Hartree-Fock model results in a very small reduction of the atomic factor at small momentum transfer with a negligible change at higher momentum transfer. Better agreement with the relativistic Hartree-Fock atomic form factor at small momentum transfer is obtained when theLS-dependent relativistic effects are included in the Breit-Pauli approximation. The sensitivity of the atomic form factor to small changes in the magnitude of the expansion coefficients of the configurational functions is also discussed.  相似文献   

16.
The lowest electronic excited state of the complexes [Ru(2,2′-bipyridine)3]2+, fac-[ClRe (CO)3(2,2′-bipyridine)], and fac-[(pyridine) Re (CO)3(2,2′-bipyridine)]+ can be quenched by methyl viologen, MV2+, N,N′-dimethyl-4,4′-bipyridinium, in fluid solutions. The quenching obeys Stern—Volmer kinetics as deduced from plots of relative luminescence quantum yield vs [MV2+], and the data are consistent with a quenching process that is essentially diffusion controlled. Pulsed laser excitation (18 ns, 354.7 nm frequency tripled Nd: YAG) of the metal complexes in the presence of MV2+ shows that a detectable fraction of the quenching results in net electron transfer to form MV+. The MV+ is detectable by resonance Raman scattering from the trailing portion of the excitation pulse. Excited state electron transfer to MV2+ from a photo-excited complex anchored to SiO2 has also been detected by transient Raman spectroscopy. High surface area SiO2 was functionalized by reaction with 4-[2-(trimethoxysilyl)ethyl]pyridine to give [SiO2]-SiEtpyr. Reaction of [SiO2]-SiEtpyr with [(CH3CN)Re(CO)3(2,2′-bipyridine)]+ then yields [SiO2]-[(SiEtpyr) Re (CO)3 (2,2′-bipyridine)]+. Electron transfer quenching of the photo-excited immobilized Re complex occurs when suspended in CH3CN solutions of MV2+ to yield MV+ as detected by resonance Raman scattering and by lifetime attenuation in the presence of MV2+.  相似文献   

17.
A classical model for electronically non-adiabatic collision processes is applied to E → V energy transfer in a collinear system, A + BC (v = 1) → A1 + BC (v = 0), resembling Br-H2.The model, which treats electronic as well as translational, rotational, and vibrational degrees of freedom by classical mechanics, describes the resonance features in this process reasonably well.  相似文献   

18.
Chemistry of indium phosphide clusters is studied using the powerful trapped ion cell techniques of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry in conjunction with an external cluster source and ion guide. The external source is capable of generating a wide range of cluster ions which the ion guide loads with high efficiency into the FTICR cell. The differential pumping of the ion guide allows for operation of the FTICR at requisite low pressure conditions while extracting clusters generated in a high pressure environment. Highly selective reactions of indium phosphide clusters are observed with ammonia and trimethylamine. Of all the InxP+y cluster sizes and stoichiometries studied, only the indium dimer ion reacts exothermically with ammonia. Thermalized In+2 reacts by indium ion transfer to ammonia. Owing to its much higher basicity, trimethylamine is much more reactive. The smaller indium phosphide clusters react by indium ion transfer to trimethylamine. As the clusters become larger, however, the reaction probability decreases to zero.  相似文献   

19.
《Polyhedron》2007,26(9-11):1773-1775
The spin density distribution of the paramagnetic [nBu4N]2[Cu(dana)] dana = N,N′-(naphthalene-2,3-diyl)-bis(oxamato) has been derived from angular dependent electron paramagnetic resonance measurements at room temperature. The results indicate a noticeable spin density transfer from the central metal to the coordinated N and O atoms. Quantum chemical studies using density functional theory reinforce the results.  相似文献   

20.
Förster resonance energy transfer (FRET) studies were carried out with CdTe quantum dots (QDs) synthesized in aqueous phase and various tetrasulfonated metallophthalocyanines (MPcS4, M = aluminum ((OH)AlPcS4), zinc (ZnPcS4), silicon ((OH)2SiPcS4) and germanium ((OH)2GePcS4) in a H2O:MeOH (1:1) solvent mixture. The QDs studied were capped with thioglycolic acid (TGA) or mercaptopropionic acid (MPA) with sizes ranging from 2.3 to 3.7 nm. Non-radiative energy transfer from QDs emission to MPcS4 complexes was observed. Study of the photophysics of the MPcs in the presence of the QDs revealed high triplet state quantum yields (ΦT, ranging from 0.41 to 0.85 in the presence of QDs), with corresponding long triplet state lifetimes (τT, which ranged from 140 to 610 μs in the presence of QDs) to allow for photosensitized reactions to occur. The efficiency of energy transfer and the donor–acceptor distance between the MPcs and the QDs were also evaluated.  相似文献   

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