Electronic States Of O2 Research Articles

Construction of BiOCl/CuBi2O4 S-scheme heterojunction with oxygen vacancy for enhanced photocatalytic diclofenac degradation and nitric oxide removal

Construction of step-scheme (S-scheme) heterojunction with superior redox ability is emerging to be an efficient way to develop high-efficiency photocatalysts for environmental pollution control. Herein, a new S-scheme heterojunction photocatalyst built from BiOCl with oxygen vacancies and CuBi2O4 was developed. Compared to pristine CuBi2O4 and BiOCl, this S-scheme heterojunction photocatalysts (BOC/CBO) show enhanced photocatalytic performance in removing aqueous diclofenac (DCF) and gaseous nitric oxide (NO) under visible light irradiation, which is mainly ascribed to the improved charge separation and transfer and redox ability by the S-scheme heterojunction structure and the enhanced catalytic oxidation by tunning the coordination structure and electronic states of O2 by oxygen vacancies. Further, the detailed DCF degradation pathways were studied and confirmed by high performance liquid chromatography–mass spectrometer (HPLC–MS). At last, a possible photocatalytic reaction mechanism based on such a S-scheme heterojunction (BOC/CBO) is proposed. This study provides an insight in constructing high-performance S-scheme heterojunction photocatalysts for environmental pollution remediation.

Excitation of the oxygen nightglow on the terrestrial planets

A scheme of excitation, quenching, and energy transfer processes in the oxygen nightglow on the Earth, Venus, and Mars has been developed based on the observed nightglow intensities and vertical profiles, measured reaction rate coefficients, and photochemical models of the nighttime atmospheres of the Venus and Mars. The scheme involves improved radiative lifetimes of some band systems, calculated yields of the seven electronic states of O2 in termolecular association, and rate coefficients of seven processes of electronic quenching of the Herzberg states of O2, which are evaluated by fitting to the nightglow observations. Electronic quenching of the vibrationally excited Herzberg states by O2 and N2 in the Earth's nightglow is a quarter of total collisional removal of the O2(A, A′) states and a dominant branch for the O2(c) state. The scheme supports the conclusion by Steadman and Thrush (1994) that the green line is excited by energy transfer from the O2(A3Σu+, v≥6) molecules, and the inferred rate coefficient of this transfer is 1.5×10−11cm3s−1. The O2 bands at 762nm and 1.27μm are excited directly, by quenching of the Herzberg states, and by energy transfer from the O2(5Πg) state. Quenching of the O2 band at 762nm excites the band at 1.27μm as well. Effective yield of the O2(a1Δg) state in termolecular association on Venus and Mars is ∼0.7. Quantitative assessments of all these processes have been made. A possible reaction of O2(c1Σu−)+CO is a very minor branch of recombination of CO2 on Venus and Mars. Night airglow on Mars is calculated for typical conditions of the nighttime atmosphere. The calculated vertical intensity of the O2 band at 1.27μm is 13kR, far below the recently reported detections.

Light-induced multiple electronic-state coupling of O2+ in intense laser fields

The dissociation processes, O2+→O++O, in intense laser fields (100 fs, ∼3×1014 W/cm2) are studied at the laser wavelength of 795 and 398 nm on the basis of the momentum imaging maps of the O+ fragment ions. The covariance map measurements are performed with high momentum resolution to assign securely the dissociation pathways. From the anisotropic momentum distribution of O+ with respect to the laser polarization direction, the electronic states of O2+ are found to be coupled exclusively through parallel transitions in the course of the dissociation process. The released kinetic energy of O+ for both 795 and 398 nm are interpreted consistently by a sequential coupling model of light-dressed potential curves of O2+ in the quartet Π state manifold.

Resonant Raman scattering in O2

Raman scattering of molecular oxygen in the region of the Schumann–Runge absorption band system is calculated from first principles in the second order of perturbation theory in the interaction of photon–electron operator. Quantitative predictions are given for the cross sections for scattering of photons and a detailed comparison is made with available measurements. The behavior of Raman spectra near the predissociating rovibronic level (v′=5,N′) in the B 3Σu− electronic state of O2 is investigated and shown to have significant dependence on the detuning of the incident laser frequency. By casting the Raman transition matrix in a form similar to the Fano formalism, we are able to investigate the nature of the resonant and nonresonant scattering in the language of configuration interaction. By varying the predissociating width of the (v′=5,N′) resonance, we make a comparison with an earlier time-dependent wave-packet analysis. We also calculate the depolarization ratio of the scattered photons parallel and perpendicular to the polarization of the incident laser beam for the different Raman branches for lines terminating in the v′′=1 and v′′=6 levels and comment on the relationship between resonant Raman scattering and fluorescence emission.

Differential cross sections for the electron impact excitation of the a1 Delta g and b1 Sigma g+ electronic states of O2

Experimental and theoretical differential cross sections for the electron impact excitation of the a1 Delta g and b1 Sigma g+ electronic states of O2 have been determined at ten incident energies ranging from 5 eV to 20 eV. The current experimental differential cross sections were obtained for the scattering range 10 degrees to 90 degrees by analysing energy loss spectra in O2 at a number of fixed scattering angles within that range. This data represents an extension to and comprehensive remeasurement of the pioneering work of Trajmar and co-workers for this scattering system. The present theoretical results were obtained using the R-matrix method with a model including nine electronic states of the target molecule and configuration interaction (CI) representations of the target wavefunctions. It represents one of the first ab initio calculations of electron scattering from an open-shell molecule.

Experimental confirmation for resonance enhancement in the electron impact excitation cross sections of the a1 Delta g and b1 Sigma g+ electronic states of O2.

In a recent publication [Phys. Rev. Lett. 68, 2011 (1992)] Noble and Burke applied the R-matrix method to low-energy electron scattering by oxygen molecules. They found that resonant contributions were made to the ${\mathit{a}}^{1}$${\mathrm{\ensuremath{\Delta}}}_{\mathit{g}}$ and ${\mathit{b}}^{1}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$ scattering cross sections, via a $^{2}\mathrm{\ensuremath{\Pi}}_{\mathit{u}}$ resonance, which significantly modified previous theoretical predictions and which were not observed in previous experiments. Here we present new results which provide the first definitive set of experimental data to confirm Noble and Burke's prediction of resonance enhancement in the electron impact excitation of the a and b electronic states.

Electron transmission studies in a free jet: molecular oxygen

A new apparatus incorporating an electron transmission spectrometer and a free jet has been used to study temporary negative-ion formation in O2. The resonant vibrational levels of the ground electronic state of O2- ( nu =4-12) were observed as spin-orbit doublets, consistent with previous experimental results. The vibrational constants of O2-, an upper bound on the autodetachment width of the nu =4 vibrational level and the relative electron attachment cross sections into the vibrational levels ( nu =5-12) have been determined. A velocity broadening term, stemming from the use of an uncollimated free jet, has also been calculated. Measurements of resonances in Ar and He were used to verify the magnitude of this term and permitted the instrument function to be extracted as well.

Vibrational intensity distributions for the various electronic states of O2+, N2+ and CO+ produced by photoionization

The vibrational intensity distributions produced by the process of photoionization are tabulated as a function of wavelength between 745 and 304 Å for all major electronic states of O 2 + , N 2 + and CO + . The technique of photoelectron spectroscopy was used with an electron energy analyzer of known luminosity.

The Spectrum of Molecular Oxygen

This is a critical review and compilation of the observed and predicted spectroscopic data on O2 and its ions O2−, O2+ and O22+ The ultraviolet, visible, infrared, Raman, microwave, and electron paramagnetic resonance spectra are included. Each electronic band system is discussed in detail, and tables of band origins and heads are given. The microwave and EPR data are also tabulated. Special subjects such as the dissociation energy of O2, perturbations, and predissociations are discussed. Potential energy curves are given, as well as f-values, Franck-Condon integrals, and other intensity factors. A summary table lists the molecular constants for all known electronic states of O2 and O2+ Electronic structure and theoretical calculations are also discussed.

FORBIDDEN TRANSITIONS IN DIATOMIC MOLECULES: II. THE ABSORPTION BANDS OF THE OXYGEN MOLECULE

The forbidden [Formula: see text] absorption bands of O2 in the near ultraviolet have been obtained under high resolution with absorbing paths up to 800 m. A detailed fine structure analysis has been carried out. It confirms the identification of the band system as a [Formula: see text] transition. Precise values of the rotational constants Bν and Dν as well as of the vibrational quanta [Formula: see text] in the upper state have been derived. Each of the "lines" of the Q branches observed under low dispersion is resolved into six components whose spacing yields the triplet splitting in the upper state. This splitting is more than twice as large as in the [Formula: see text] ground state and is of opposite sign. The splitting constants λ and γ have been determined and their variation with the vibrational quantum number observed. In addition to the Q-form branches weak O- and S-form branches have been found in agreement with the prediction of Present which is based on the assumption that spin–orbit coupling is the main cause for the occurrence of this forbidden transition. However, the relative intensities of the different branches deviate strongly from Present's prediction. The dissociation limit obtained from the convergence limit of the bands (without extrapolation) is at 41219 ± 40 cm.−1 This value is higher by about 220 cm.−1 than the value of the dissociation energy of O2 derived from the Schumann–Runge bands. It is possible that the limit of the Schumann–Runge bands, which is based on a short extrapolation, and therefore the value of the dissociation energy of O2 has to be slightly revised. The electron configurations and dissociation products of the various electronic states of O2 are briefly discussed.