Np Transitions Research Articles

Analyzing the Intensities of K-Edge Transitions in X2 Molecules (X = F, Cl, Br) for Use in Ligand K-Edge X-ray Absorption Spectroscopy.

Ligand K-edge X-ray absorption spectroscopy (XAS) is regularly used to determine the ligand contribution to metal-ligand bonds. For quantitative studies, the pre-edge transition intensities must be referenced to an intensity standard, and pre-edge intensities obtained from different ligand atoms cannot be compared without standardization due to different cross sections at each absorption edge. In this work, the intensities of the 1s → σ* transitions in F2, Cl2, and Br2 are analyzed for their use as references for ligand K-edge XAS. We show that the intensities of these transitions are equal to the intensities of the 1s → np transitions in the unbound halogens. This finding is supported by a comparison between the normalized experimental intensities for the molecules and the calculated oscillator strengths for the atoms. These results highlight the potential for these molecules to be used as intensity standards in F, Cl, and Br K-edge XAS experiments.

Experimental and computational VUV photoabsorption study of dimethyl carbonate: A green solvent

VUV photoabsorption spectrum of dimethyl carbonate in the energy region 7–11 eV and its complete spectral analysis with the aid of quantum chemical calculations is reported for the first time. The spectrum recorded using synchrotron radiation comprises of weak bands overlapping a broad intense continuum. With a view to interpret possible vibronic structure, gas phase infrared spectrum in the region 500–4000 cm−1 is revisited. Density functional theory (DFT) and time dependent DFT (TDDFT) methodologies are used to obtain ground state geometry, vibrational frequencies and vertical excitation energies of dimethyl carbonate. The intense broad features in the spectrum could be attributed to valence transitions. Based on quantum defect calculations, energy ordering and symmetry, weak bands are designated as ns, np and nd type Rydberg transitions converging to the first five ionization potentials. The highest occupied molecular orbital is nonbonding in nature and largely localized on the oxygen atom of carbonyl group and quantum defect values obtained are consistent with excitation from oxygen lone pair. Excellent correlation is obtained between theoretically predicted (CAM-B3LYP levels of theory) and experimentally observed excited state energies. Potential energy curves of ground and first few excited states generated with a view to provide additional insights into their nature and further describe the observed spectra. The present study provides a comprehensive experimental and computation analysis of the VUV photoabsorption spectroscopy of dimethyl carbonate.

Selective Hydrogen Isotope Separation via Breathing Transition in MIL-53(Al)

Breathing of MIL-53(Al), a flexible metal-organic framework (MOF), leads to dynamic changes as narrow pore (np) transitions to large pore (lp). During the flexible and reversible transition, the pore apertures are continuously adjusted, thus providing the tremendous opportunity to separate mixtures of similar-sized and similar-shaped molecules that require precise pore tuning. Herein, for the first time, we report a strategy for effectively separating hydrogen isotopes through the dynamic pore change during the breathing of MIL-53(Al), arepresentative of flexible MOFs. The experiment shows that the selectivity for D2 over H2 is strongly related to the state of the pore structure of MIL-53(Al). The highest selectivity (SD2/H2 = 13.6 at 40 K) was obtained by optimizing the exposure temperature, pressure, and time to systematically tune the pore state of MIL-53(Al).

Competition between radiative and Auger decay processes of doubly excited Li-like C, N and O ions

SynopsisWe performed charge exchange collision experiments of metastable He-like C, N and O ions (1s2s 3S1) with neutral target gases, and observed soft X-rays from doubly excited Li-like C, N and O ions produced by single electron capture. These emissions corresponded to 1s22s 1S0 - 1s2s (3S1) np transitions according to calculations for transition energies by the Cowan code.

Precision spectroscopy of 2S–nP transitions in atomic hydrogen for a new determination of the Rydberg constant and the proton charge radius

Precision measurements of transition frequencies in atomic hydrogen provide important input for a number of fundamental applications, such as stringent tests of QED and the extraction of fundamental constants. Here we report on precision spectroscopy of the 2S–4P transition in atomic hydrogen with a reproducibility of a few parts in 1012. Utilizing a cryogenic beam of hydrogen atoms in the metastable 2S state reduces leading order systematic effects of previous experiments of this kind. A number of different systematic effects, especially line shape modifications due to quantum interference in spontaneous emission, are currently under investigation. Once fully characterized, our measurement procedure can be applied to higher lying 2S–nP transitions () and we hope to contribute to an improved determination of the Rydberg constant and the proton root mean square charge radius by this series of experiments. Ultimately, this improved determination will give deeper insight into ‘the proton size puzzle’ from the electronic hydrogen side.

Excited states of aniline by photoabsorption spectroscopy in the 30 000–90 000 cm−1 region using synchrotron radiation

The photoabsorption spectrum of aniline (C6H5NH2) in gas phase in the 30,000-90,000 cm(-1) (3.7-11.2 eV) region is recorded at resolution limit of 0.008 eV using synchrotron radiation source for the first time to comprehend the nature of the excited valence and Rydberg states. The first half of the energy interval constitutes the richly structured valence transitions from the ground to excited states up to the first ionization potential (IP) at 8.02 eV. The spectrum in the second half consists of vibrational features up to second IP (9.12 eV) and structureless broad continuum up to the third IP (10.78 eV). The electronic states are assigned mainly to the singlets belonging to π → π* transitions. A few weak initial members of Rydberg states arising from π → 4s, np or nd transitions are also identified. Observed vibrational features are assigned to transitions from the ground state A' to the excited states 1A", 3A', 5A", 6A', and 10A" in C(s) symmetry. Time dependent density functional theory (TDDFT) calculations at B3LYP level of theory are employed to obtain the vertical excitation energies and the symmetries of the excited states in equilibrium configuration. The computed values of the transition energies agree fairly well with the experimental data. Further the calculated oscillator strengths are used to substantiate the assignments of the bands. The work provides a comprehensive picture of the vacuum ultraviolet photoabsorption spectrum of aniline up to its third ionization limit.

Spectral lines behavior of Be I and Na I isoelectronic sequence in Debye plasma environment

We report the plasma screening effect on the first ionization potential (IP) and [He]2s2 (1S0)→[He]2s2p/2s3p allowed (P11) and inter-combination transitions (P31) in some selected Be-like ions. In addition, we investigate the spectral properties of [Ne]3s (2S1/2)→[Ne]np (2P1/2 and P23/2 for n = 3, 4) transitions in Ca X and Fe XVI ions (Na I isoelectronic sequence) and [He]3s(2S1/2)→[He]np (2P1/2 and P23/2 for n = 2, 3) transitions in Li, B II, and N IV (Li I isoelectronic sequence) under plasma environment. The state-of-the-art relativistic coupled cluster calculations using the Debye model of plasma for electron-nucleus interaction show that (a) the ionization potential decreases sharply with increasing plasma strength and (b) the gap between the [He]2s2 (1S0)→[He]2s2p(1,3P1) energy levels increases with increasing plasma potential and nuclear charge. It is found that the [He]2s2 (1S0)→2s3p (1,3P1) transition energy decreases uniformly with increasing plasma potential and nuclear charge. In other words, the spectral lines associated with 2s-2p (i.e., Δn=0, where n corresponds to principle quantum number) transitions in Be I isoelectronic sequence exhibit a blue-shift (except for Be I, B II, and the lowest inter-combination line in C III, which exhibit a red-shift), whereas those associated with 2s-3p (i.e., Δn≠0) transitions are red-shifted. Similar trend is observed in Li I and Na I isoelectronic sequences, where spectral lines associated with Δn=0 (Δn≠0) are blue-shifted (red-shifted). The effect of Coulomb screening on the spectral lines of ions subjected to plasma is also addressed.

Stark halfwidth trends along the homologous sequence of doubly ionized noble gases

Aims. The aim of this work is to analyse experimental Stark halfwidths behaviour for the ( 3 P)ns−( 3 P)np and ( 3 P)np−( 3 P)nd transitions along the homologous sequence of single ionized noble gases. This kind of trend analysis can be useful for Stark halfwidths predictions and therefore for spectroscopic diagnostic of astrophysical plasmas. Methods. The compilation of Stark halfwidths was done taking into account the measurements developed in the last decades. The experimental results and observed Stark halfwidth trends for different multiplets of ionized noble gases were compared with the modified semiempirical formula (MSE) calculations and other theoretical estimations. Results. The analysis shows that the halfwidths of the spectral lines in all observed multiplets belonging to the same transitions have a similar trend along the homologous sequence. Stark halfwidths of ( 3 P)ns−( 3 P)np transitions are more or less constant, while those of ( 3 P)np−( 3 P)nd transitions have a clear increasing slope. A qualitative explanation of the observed Stark halfwidth trends based on the energy level structure is also given.

Theoretical study on the 1s22s-1s2 np transitions for Ni25+ ion

The transition energies, wavelengths and oscillator strengths for the 1s22s-1s2np (n ⩽ 9) transitions of Ni25+ ion are calculated. In calculation of the energies, we not only take account of the firstorder corrections from relativistic and mass-polarization effects, but also estimate the higher-order relativistic contribution and QED correction by introducing the effective nuclear charge. The results agree with experimental data available in literature satisfactorily. Grotrian diagram showing these transitions is given.

Theoretical study on behaviors of 1s22s-1s2 np transition for Co24+ ion in the whole energy region

Non-relativistic energies of 1s22s and 1s2 np (n⩽9) states for Co24+ ion are calculated by using the full-core plus correlation method. Our results of 1s22s and 1s22p states agree well with the high-precision results of Yan et al. Based on calculating the first-order corrections to the energy from relativistic and mass-polarization effects, we estimate the higher-order relativistic contribution and QED correction to the energy under a hydrogenic approximation. The transition energies, wavelengths and oscillator strengths for the 1s22s−1s2 np (n⩽9) transitions of this ion are calculated. The results agree with the experimental data available in literature satisfactorily. By combining with quantum defect theory, our theoretical predictions on the energy and oscillator strength of this ion are extrapolated to the whole energy region including continuous states.

Medium and high resolution vacuum UV photoabsorption spectroscopy of methyl iodide (CH 3I) and its deuterated isotopomers CD 3I and CH 2DI. A Rydberg series analysis

The vacuum UV photoabsorption spectrum of CH 3I has been investigated between 5 eV and 20 eV. Numerous vibronic transitions are observed. In the high 10–20 eV photon energy range weak to very weak diffuse bands are observed and ascribed to electronic transitions from 3a 1, 1e and 2a 1 to Rydberg orbitals. In the 6–10.5 eV photon energy range more than 200 sharp and strong to weak lines have been observed. Several photon energy ranges were explored under high resolution conditions allowing us to observe many series up to high values of the principal quantum number n. They are assigned to vibrationless Rydberg transitions and classified into two groups converging to the two components of the spin–orbit split X ˜ 2 E state of CH 3I +. These two groups consist of six different Rydberg series, i.e., nsa 1, npa 1, npe, nda 1, nde and nf. A very close correlation has been established between the term values of the Rydberg states in CH 3I and in Xe for ns, np, nd and nf Rydberg transitions. For the first time, the same measurements have been performed and the interpretation has been proposed for the photoabsorption spectrum of CH 2DI and CD 3I in the 6–10.5 eV photon energy range. For these two species, ionization energies are deduced: for the X ˜ 2 E 3/2 and X ˜ 2 E 1/2 states of CH 2DI, these are IE ad = 9.544 eV and IE ad = 10.168 eV, respectively, and the corresponding energies are 9.552 eV and 10.173 eV in CD 3I.

Oscillator strengths for 2 2S–n2 P transitions of the lithium isoelectronic sequence from Z = 11 to 20

The dipole-length, dipole-velocity and dipole-acceleration absorption oscillator strengths for the 1s22s–1s2 np (3 ≤ n ≤ 9) transitions of lithium-like systems from Z = 11 to 20 are calculated by using the energies and the multi-configuration interaction wave functions obtained from a full core plus correlation method, in which relativistic and mass-polarization effects on the energy, as the first-order perturbation corrections, are included. The results of three forms are in good agreement with each other, and closely agree with the experimental data available in the literature. Based on the quantum defects obtained with quantum defect theory (QDT), the discrete oscillator strengths for the transitions from the ground state to highly excited states 1s2 np (n ≥ 10) and oscillator strength densities corresponding to the bound-free transitions are obtained for these ions.

Cumulative contributions of 3s–np (n⩾3) transitions in comparing O atom densities in low-pressure Ar–O2 and He–O2 glow discharges

Many-fold enhancements in the population densities of O atoms in low-pressure glow discharges in Ar–O2 and He–O2 compared with the discharge in pure O2 have been reported in recent years. In some reports, the 3sS3,5–3pP3,5 transitions of O atoms around 844.6 or 777.2nm are considered in estimating the density of atomic oxygen. The authors’ results demonstrate that the contributions of other possible transitions such as 3sS3,5–npP3,5 (n>3) directly feeding the lower 3sS3,5 levels are also significant and should be included for a better estimate of O atom densities.

Temperature-sensitive line ratio diagnostics based on Si satellite-to-resonance line ratios for 1s 2–1s np transitions

Dielectronic satellite lines due to 1s 2 n′l′–1s np n′l′ ( n = 3, 4) transitions in Li-like Si (Si XII) occur at 5.818 and 5.565 Å, on the long wavelength side of the He-like Si (Si XIII) 1s 2–1s3p and 1s 2–1s4p lines at 5.681 and 5.384 Å, respectively. They have been extensively observed with the RESIK crystal spectrometer on the Russian spacecraft CORONAS-F. As with corresponding satellites 1s 2 nl–1s2p nl on the long-wavelength side of the Si XIII 1s 2–1s2p resonance line, there is an inverse temperature dependence of the intensity ratio of the satellites to the He-like ion lines ( I sat/ I He). New atomic data are used to calculate the Si XII satellite line intensities and thus the I sat/ I He ratio. RESIK observations of the ratio in solar flares, together with temperatures from the ratio of the two GOES X-ray channels, are compared with theoretical variation of the ratio with temperature. The good agreement indicates this to be a valuable temperature diagnostic for solar flares and laboratory plasmas such as tokamaks. There are implications for similar satellites in Fe line spectra which are observed with broad-band resolution by the RHESSI solar flare mission.

The application of the single-channel random phase approximation to radiative properties of dense He and Li plasmas

We performed single-channel, single-component random phase approximation calculations for dense He and Li plasmas for an electron temperature of kT=10 eV . Results are presented for excitation energies and oscillator strengths for the (1,2)s−np (n=2−5) transitions using both the ion-sphere and ion-correlation (IC) models. Our results indicate that ion correlations are not a significant effect for these systems and conditions.

Observation of atomiclike electronic excitations in pure 3He and 4He clusters studied by fluorescence excitation spectroscopy.

The structure of the electronically excited states of 3He and 4He clusters is investigated using fluorescence excitation spectroscopy. Distinct bands are observed energetically close to atomic 1s-ns, nd, np transitions and attributed to perturbed excited He atomiclike states with different principle and orbital quantum numbers. The line shifts and widths of the bands of 3He and 4He clusters of the same size are different and correlate with the average particle density inside the clusters calculated using the density functional method.

Rise and fall of the 4d10-->4d94f resonance in the Xe isoelectronic sequence.

The extreme ultraviolet photoabsorption spectrum of a laser-produced lanthanum plasma has been recorded and found to contain a number of discrete features in the 130-eV region. These have been analyzed as 4${\mathrm{d}}^{10}$\ensuremath{\rightarrow}4${\mathrm{d}}^{9}$nf,np transitions in ${\mathrm{La}}^{3+}$. We show that the 4f transition, which is expected to be the strongest, is not in evidence. The reason is that this resonance, after the collapse of the 4f wave function, has a large autoionization width. We conclude that the 4f orbital in ${\mathrm{Ba}}^{2+}$ is only partially collapsed, which settles a long-standing discussion of this point.

Vacuum ultraviolet absorption cross sections of SiH4, GeH4, Si2H6, and Si3H8

The vacuum ultraviolet absorption cross sections of SiH4, GeH4, Si2H6, and Si3H8 are reported for the wavelength region 107–220 nm using synchrotron radiation as a light source. Absorption maxima of these compounds were found at the exciting wavelengths of 115–119 nm. Broad peaks observed were mostly assigned as primarily Rydberg transitions of the σSiH and σSiSi bonding electrons to the 4s, 4p, and 4d orbitals. The absorption features of germane resemble those of monosilane. In the photoexcitation of monosilane, the emission of the SiH(Ã 2Δ→X̃ 2Π) transition was observed and its onset was found to be 132±2nm. The absorption spectrum of disilane showed five peaks. They were mostly assigned as 2a1g→4s, 2a1g→np(n=4−6) transitions and the strongest band was overlapped by 1eg→4d and 1eu→4p Rydberg transitions. In trisilane molecules three very weak and broad peaks were recognized and assigned as 3b2→4s, 4p and 4a1→4s, 4d Rydberg transitions. The strongest band was tentatively assigned as the superposition of 1a2→4d and 3a1→4p Rydberg excitations.

Observation of exciton-exciton scattering in Cu2O by time-resolved photomodulation spectroscopy.

Transient photomodulation techniques with picosecond laser pulses have been applied to make contact with excitonic scattering through several nP transitions of the yellow exciton series in ${\mathrm{Cu}}_{2}$O. We show first how this experimental approach can be generally useful in the dynamical study of collisionally broadened free-exciton resonances, and then argue that the observed time-dependent spectra give direct information about the energy-dependent character of nP-1S exciton scattering events in ${\mathrm{Cu}}_{2}$O under conditions of weak photoexcitation considered here.

Electronic Structure of Deep-Lying Sulfur Centers in Si

AbstractA theoretical analysis has been made of infrared absorption spectra measured earlier for four deep-lying sulfur centers in Si. The data consist of absorption frequencies and polarization selection rules determined for uniaxial stress applied along [001], [111], and [110] axes. Both ls + np transitions and ls → ls transitions are observed. The A and B centers (binding energies 0.1090 eV and 0.1872 eV, respectively) are found to be He-like, while the C and D centers (binding energies 0.3683 eV and 0.6116 eV, respectively) are found to be He+-like. The D center spectra are consistent with Td symmetry, while the A, B and C spectra are consistent in most respects with C3v or D3d symmetry. One noteworthy result is the finding that the ls + np spectral frequencies observed under stress for the A center are consistent with a ls(E) ground state.