Ultraviolet Transitions Research Articles

229ThF4 thin films for solid-state nuclear clocks.

After nearly 50 years of searching, the vacuum ultraviolet 229Th nuclear isomeric transition has recently been directly laser excited1,2 and measured with high spectroscopic precision3. Nuclear clocks based on this transition are expected to be more robust4,5 than and may outperform6,7 current optical atomic clocks. These clocks also promise sensitive tests for new physics beyond the standard model5,8-12. In light of these important advances and applications, a substantial increase in the need for 229Th spectroscopy targets in several platforms is anticipated. However, the growth and handling of high-concentration 229Th-doped crystals5 used in previous measurements1-3,13,14 are challenging because of the scarcity and radioactivity of the 229Th material. Here we demonstrate a potentially scalable solution to these problems by performing laser excitation of the nuclear transition in 229ThF4 thin films grown using a physical vapour deposition process, consuming only micrograms of 229Th material. The 229ThF4 thin films are intrinsically compatible with photonics platforms and nanofabrication tools for integration with laser sources and detectors, paving the way for an integrated and field-deployable solid-state nuclear clock with radioactivity up to three orders of magnitude smaller than typical 229Th-doped crystals1-3,13. The high nuclear emitter density in 229ThF4 also potentially enables quantum optics studies in a new regime. Finally, we present the estimation of the performance of a nuclear clock based on a defect-free ThF4 crystal.

Absolute nuclear charge radius by Na-like spectral line separation in high-Z elements

Abstract We describe a novel technique to determine absolute nuclear radii of high-Z nuclides. Utilizing accurate theoretical atomic structure calculations together with precise measurements of extreme ultraviolet transitions in highly charged ions this method allows for precise determinations of absolute nuclear charge radii based upon the well-known nuclear radii of their neighboring elements. This method can work for elements without stable isotopes, and its accuracy may be competitive with current methods (electron scattering and muonic x-ray spectroscopy).

Atomic Transition Probabilities for Ultraviolet and Optical Lines of Tm ii * *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555 (program GO-15657). This paper also includes data gathered with the 6.5 m Magellan Telescopes

We report new branching fraction measurements for 224 ultraviolet and optical transitions of Tm ii. These transitions range in wavelength (wavenumber) from 2350 to 6417 Å (42,532–15,579 cm−1) and originate in 13 odd-parity and 24 even-parity upper levels. Thirty-five of the 37 levels, accounting for 213 of the 224 transitions, are studied for the first time. Branching fractions are determined for two levels studied previously for comparison to earlier results. The levels studied for the first time are high lying, ranging in energy from 35,753 to 54,989 cm−1. The branching fractions are determined from emission spectra from two different high-resolution spectrometers. These are combined with radiative lifetimes reported in an earlier study to produce a set of transition probabilities and log(gf) values with accuracy ranging from 5% to 30%. Comparison is made to experimental and theoretical transition probabilities from the literature where such data exist. These new log(gf) values are used to derive an abundance from one previously unused Tm ii line in the UV spectrum of the r-process-enhanced metal-poor star HD 222925, and this abundance is consistent with previous determinations based on other Tm ii lines.

Ultraviolet electroluminescence with electrically tunable colour from epitaxial n-(0001)ZnO/p-(0001)GaN light-emitting diodes

Pulsed laser deposition technique is used to grow unintentionally n-type (0001)ZnO layers with high crystalline and morphological qualities on p-type (0001)GaN/sapphire templates. Electroluminescent devices are fabricated on these p–n heterojunctions. Oxygen pressure during growth has been found to influence strongly the crystalline and defect properties of the grown layers, which affect not only the current–voltage characteristics but also the emission properties of the electroluminescent devices. It has been observed that the electroluminescence (EL) spectra have both defects related visible and band-edge related ultraviolet (UV) transition features stemming from both GaN and ZnO sides. The study reveals that UV to visible EL intensity ratio maximizes at an optimum oxygen pressure. The relative contribution of EL originating from ZnO and GaN sides can be tuned by the applied bias, as the bias can control the depletion width and hence the carrier interdiffusion across the junction. This finding thus offers a scope to electrically tune the colour of the emitted light in these devices.

Unraveling photodissociation dynamics by sub-femtosecond ultraviolet pulses: insights into fragmental kinetics and carrier-envelope phase characterization

The duration of laser pulses and the carrier-envelope phase (CEP) play a crucial role in shaping kinetic energy release (KER) spectra. In this study, we performed theoretical calculations on pulse duration-dependent KER spectra, ranging from hundreds to sub-femtoseconds, focusing on the MgH+ scenario. Our findings reveal a distinct shift in KER peaks from sub-cycle pulses, deviating from the resonance energy. Utilizing two-level perturbation theory, we identify that this shift is attributable to the energy-dependent transition matrix elements. Moreover, our investigation uncovers a notable CEP effect in KER from sub-cycle pulses, arising from interference between counter-rotating and rotating terms within a single ultraviolet photon transition. To leverage this insight, we propose a novel pump-probe methodology for precise CEP characterization of ultra-short laser pulses. We hope this method would promise advancements in understanding and manipulating ultrafast processes.

Piezoelectricity activates persulfate for water treatment: A perspective

Advanced oxidation processes (AOPs) utilizing persulfate (PS) offer great potential for wastewater treatment. Yet, the dependency on energy and chemical-intensive activation techniques, such as ultraviolet radiation and transition metal ions, constrains their widespread adoption. Recognizing this limitation, researchers are turning towards the piezoelectric effect—a novel, energy-efficient method for PS activation that capitalizes on the innate piezoelectric characteristics of materials. Intriguingly, this method taps into weak renewable mechanical forces omnipresent in nature, ranging from wind, tides, water flow, sound, and atmospheric forces. In this perspective, we delve into the burgeoning realm of piezoelectric/PS-AOPs, elucidating its fundamental principles, the refinement of piezoelectric materials, potential mechanical force sources, and pertinent application contexts. This emerging technology harbors significant potential as a pivotal element in wastewater pretreatment and may spearhead innovations in future water pollution control engineering.

Subrecoil cooling of 6Li atoms by 2S→3P ultraviolet narrow transition

Subrecoil cooling of 6Li atoms by 2S→3P ultraviolet narrow transition

Laboratory Study of the Cameron Bands and UV Doublet in the Middle Ultraviolet 180–300 nm by Electron Impact upon CO2 with Application to Mars

We have observed electron impact fluorescence from CO2 to excite the Cameron bands (CBs), CO (a 3Π → X 1Σ+; 180–280 nm), the first-negative group (1NG) bands, CO+ (B 2Σ+ → X 2Σ+; 180–320 nm), the fourth-positive group (4PG) bands, CO (A 1Π → X 1Σ+; 111–280 nm), and the UV doublet, CO2 + ( 288.3 and 289.6 nm) in the ultraviolet (UV). This wavelength range matches the spectral region of past and present spacecraft equipped to observe UV dayglow and aurora emissions from the thermospheres (100–300 km) of Mars and Venus. Our large vacuum system apparatus is able to measure the emission cross sections of the strongest optically forbidden UV transitions found in planetary spectra. Based on our cross-sectional measurements, previous CB emission cross-sectional errors exceed a factor of 3. The UV doublet lifetime is perturbed through spin–orbit coupling. Forward modeling codes of the Mars dayglow have not been accurate in the mid-UV due to systematic errors in these two emission cross sections. We furnish absolute emission cross sections for several band systems over electron energies 20–100 eV for CO2. We present a CB lifetime, which together with emission cross sections, furnish a set of fundamental physical constants for electron transport codes such as AURIC (Atmospheric Ultraviolet Radiance Integrated Code). AURIC and Trans-Mars are used in the analysis of UV spectra from the Martian dayglow and aurora.

Ultraviolet and infrared spectra of mono-, di- and tri-hydrated clusters of protonated noradrenaline – Solvation and conformational variations

Ultraviolet (UV) and infrared (IR) spectra of hydrated clusters of protonated noradrenaline (NAdH+) are measured by the electrospray – cold ion trap laser spectroscopy. NAdH+-(H2O)1,2 show complicated UV transitions, while NAdH+-(H2O)3 gives simple and blue-shifted spectrum. Conformer-selected IR spectra and the IR-UV hole burning spectra reveal that 4, 3 and 2 conformers coexist in hydrated complexes of n = 1 ∼ 3, respectively. Gauche conformations for all observed conformers are assigned from the comparison to the theoretical IR spectra obtained by the DFT calculations. The blue shift in NAdH+-(H2O)3 is rationalized by the πσ*interaction between the third water to OH in catechol.

Electronically Excited Complex Formation in Magnesium Cluster-Halogen Atom Reactions.

A near ultraviolet transition of Mg2F has been observed in emission from the reaction between magnesium clusters, most likely Mg3, and fluorine atoms. Because there is little evidence for upper-state internal excitation, the spectrum is assigned assuming that the upper state is quenched to its lowest vibrational levels. Two of possibly three ground-state vibrational frequencies, υ1 = 516 ± 10 cm-1 and υ2 = 104 ± 10 cm-1, have been established. Dispersed laser-induced fluorescence studies extrapolating on the observed chemiluminescence indicate an excited-state symmetric stretch frequency of order 370 ± 30 cm-1. Electronic structure calculations at the CCSD(T)/CBS level predict that the ground state of Mg2F has C2v symmetry and can be described as an Mg2+F- ion pair with two Mg-F bonds. Like the MgF A-X transition that is largely a transition between Mg orbitals, the observed transition in Mg2F is largely between orbitals on the magnesium dimer ion. The asymmetric C∞v Mg2+F- complex is also a minimum and is predicted to be 6.7 kcal/mol higher in energy. Calculated structures for the Mg2Cl isomers are also presented and used to further interpret the experimental results for the reaction of Mg clusters with Cl atoms. In contrast to Mg2F, the ground state of Mg2Cl is a linear C∞v MgMgCl structure with the C2v and D∞h isomers of the MgClMg structure slightly higher in energy.

Z -dependent crossing of excited-state energy levels in highly charged galliumlike lanthanide atomic ions

Extreme ultraviolet (EUV) optical transitions of lanthanide highly charged ions have been studied. The $[\mathrm{Ni}]4{s}^{2}4p--[\mathrm{Ni}]4{s}^{2}4d$ and $[\mathrm{Ni}]4{s}^{2}4p--[\mathrm{Ni}]4s4{p}^{2}$ transition lines of galliumlike lanthanide elements have been spectroscopically measured in large helical device (LHD) plasma and electron-beam ion trap (EBIT) plasma. The wavelengths for Eu ions agreed within $0.03%$ between the LHD and EBIT measurements. Due to the enhancement of spin-orbit interactions along with the increase of atomic number $Z$ in $4p$ atomic orbitals, energy splitting between $4{p}_{1/2}$ and $4{p}_{3/2}$ orbitals increases significantly from lanthanum to lutetium, causing the crossing of $Z$-dependent wavelength curves. The spectral line positions and strengths are theoretically calculated by means of the multiconfiguration Dirac-Fock method. The mixing of the $[\mathrm{Ni}]4{s}^{2}4d$ and $[\mathrm{Ni}]4s4{p}^{2}$ configurations leads to an avoided crossing in the apparent wavelength curves. The configuration mixing makes both the $[\mathrm{Ni}]4{s}^{2}4p--[\mathrm{Ni}]4{s}^{2}4d$ and $[\mathrm{Ni}]4{s}^{2}4p--[\mathrm{Ni}]4s4{p}^{2}$ lines well visible in the EUV spectra near the level crossing point. The levels are found to cross between $Z=62$ and 63.

Exciton decay mechanism in DNA single strands: back-electron transfer and ultrafast base motions.

The photochemistry of DNA systems is characterized by the ultraviolet (UV) absorption of π-stacked nucleobases, resulting in exciton states delocalized over several bases. As their relaxation sensitively depends on local stacking conformations, disentangling the ensuing electronic and structural dynamics has remained an experimental challenge, despite their fundamental role in protecting the genome from potentially harmful UV radiation. Here we use transient absorption and transient absorption anisotropy spectroscopy with broadband femtosecond deep-UV pulses (250–360 nm) to resolve the exciton dynamics of UV-excited adenosine single strands under physiological conditions. Due to the exceptional deep-UV bandwidth and polarization sensitivity of our experimental approach, we simultaneously resolve the population dynamics, charge-transfer (CT) character and conformational changes encoded in the UV transition dipoles of the π-stacked nucleotides. Whilst UV excitation forms fully charge-separated CT excitons in less than 0.3 ps, we find that most decay back to the ground state via a back-electron transfer. Based on the anisotropy measurements, we propose that this mechanism is accompanied by a structural relaxation of the photoexcited base-stack, involving an inter-base rotation of the nucleotides. Our results finally complete the exciton relaxation mechanism for adenosine single strands and offer a direct view into the coupling of electronic and structural dynamics in aggregated photochemical systems.

Translesion Synthesis Past 5-Formylcytosine-Mediated DNA-Peptide Cross-Links by hPolη Is Dependent on the Local DNA Sequence.

DNA-protein cross-links (DPCs) are unusually bulky DNA lesions that form when cellular proteins become trapped on DNA following exposure to ultraviolet light, free radicals, aldehydes, and transition metals. DPCs can also form endogenously when naturally occurring epigenetic marks [5-formyl cytosine (5fC)] in DNA react with lysine and arginine residues of histones to form Schiff base conjugates. Our previous studies revealed that DPCs inhibit DNA replication and transcription but can undergo proteolytic cleavage to produce smaller DNA-peptide conjugates. We have shown that 5fC-conjugated DNA-peptide cross-links (DpCs) placed within the CXA sequence (X = DpC) can be bypassed by human translesion synthesis (TLS) polymerases η and κ in an error-prone manner. However, the local nucleotide sequence context can have a strong effect on replication bypass of bulky lesions by influencing the geometry of the ternary complex among the DNA template, polymerase, and the incoming dNTP. In this work, we investigated polymerase bypass of 5fC-DNA-11-mer peptide cross-links placed in seven different sequence contexts (CXC, CXG, CXT, CXA, AXA, GXA, and TXA) in the presence of human TLS polymerase η. Primer extension products were analyzed by gel electrophoresis, and steady-state kinetics of the misincorporation of dAMP opposite the DpC lesion in different base sequence contexts was investigated. Our results revealed a strong impact of nearest neighbor base identity on polymerase η activity in the absence and presence of a DpC lesion. Molecular dynamics simulations were used to structurally explain the experimental findings. Our results suggest a possible role of local DNA sequence in promoting TLS-related mutational hot spots in the presence and absence of DpC lesions.

A global line list for HDO between 0 and 35000 cm[formula omitted] constructed using multiphoton spectra

Multiphoton spectroscopy of monodeuterated water is employed to determine more than 210 new energy levels of HDO in the 25 000–35 000 cm−1 region. These new empirical energy levels are used to fit a potential energy surface (PES) valid between 20 000 cm−1 and 35 000 cm−1. Using this PES and an accurate lower energy PES as starting points, an energy-switching surface is constructed which is capable of reproducing the whole HDO spectrum from 0 to 35 000 cm−1. This PES is used to calculate a line list for HDO which covers infra red, visible and near ultraviolet transitions.

Band structure and ultraviolet optical transitions in ErN

Erbium nitride (ErN) is a rare-earth metal mononitride continuing to receive interest due to its unique electronic, magnetic, and optical properties. ErN has shown promise in the development of new functional materials for optoelectronic and spintronic devices. Here, we report on the optical properties of ErN crystals, grown by sublimation and probed by photoluminescence (PL) spectroscopy at both room temperature and 180 K. Multiple transition lines were observed between 2 and 4.5 eV. Using the PL results together with reported calculations, a coherent picture for the band structure at the Γ-point for ErN crystals was derived. PL results revealed that ErN has a minimum direct energy gap of 2.41 eV and a total of two valence bands and two conduction bands at the Γ-point separated by about 0.15 eV and 0.34 eV, respectively. These transitions reveal optical properties of ErN in the UV region and its band structure at the Γ-point.

Spectroscopic study of EUV and SXR spectral lines with partition function and level population of W LVI

We present a comprehensive and elaborate study of W LVI (K-like W55+) by using multi-configuration Dirac–Fock method (MCDF). We have included relativistic corrections, QED (quantum electrodynamics) and Breit corrections in our computation. We have reported energy levels and radiative data for multipole transitions (i.e., electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2)) within the lowest 142 fine-structure levels and predicted soft X-ray transition (SXR) and extreme ultraviolet transitions (EUV) from higher excited states to the ground state. We have compared our calculated data with energy levels compiled by NIST and other available results in the literature and the small discrepancies found with them are discussed. Because only a few of the lowest levels are available in the literature, for checking excitation energies of higher excited states we have performed the same calculations with the distorted wave method. Furthermore, we have also provided relative population for the first five excited states, with both the partition function and thermodynamic quantities for W LVI and studied their variations with temperature. We believe that our reported new atomic data of W LVI may be useful in identification and analysis of spectral lines from various astrophysical and fusion plasma sources and may also be beneficial in plasma modeling.

Reevaluation of Cr6+ optical transitions through Gd2O3 doping of chromium-borate glasses

Abstract Chromium-doped borate glasses are appealing for potential optical applications as they feature distinct optical transitions in the visible and ultraviolet spectral regimes. However, such intense UV transitions are often screened in borate glasses due to their proximity to the bulk absorption edge. Here, we utilize variable concentrations of the wide band gap Gd2O3 dopant to detach these near-edge optical transitions. The amorphous nature of all Gd2O3-doped borate glass samples, containing a fixed Cr amount, was confirmed by X-ray diffraction. Gd2O3 additives were found to enforce the compactness of the glassy network as inferred from the increased experimental density and calculated average boron-boron separation. Analysis of the infrared spectra revealed the essential vibration modes of structural units, the non-bridge oxygen, and the fraction of tetrahedrally-coordinated boron atoms ratios. These ratios together with a noticeable BO3 to BO4 conversion suggest an open glass structure with enlarged band gap energy. The latter is confirmed by recording the optical absorption spectra for all samples, which exhibited clear blue shifts of the absorption edge and an estimated wide band gap of size ~3.38 eV. In addition to Cr3+ transitions manifesting in the visible region, two well-resolved ultra-violet transitions characteristic for Cr6+ were unambiguously identified down to ~339 nm. These transitions and other relevant quantities, such as crystal field strength and Racah parameters, were accurately determined from a deconvolution process applied to all optical spectra. The present Gd2O3-doped glasses offer wide band gap materials with high energy optical transitions suitable for UV optics, such as ultraviolet digital photography and insect light traps.

High-resolution spectroscopy of the hot Am star HR 3383

ABSTRACT We present the spectrum analysis of the hot Am star HR 3383 (A1 Vm). Hubble Space Telescope STIS and Nordic Optical Telescope SOFIN data are modelled with synthetic spectra, and abundances are investigated for 78 elements. Most light elements up through oxygen show deficiencies, compared to solar abundances, followed by the general trend of increasing abundance enhancement with atomic number that levels off at a 30-fold enhancement at the lanthanide group and heavier elements. The derived element distribution is generally consistent with what is observed in other hot Am stars. Abundances for HR 3383 are also similar to what is seen for the cooler HgMn stars, with the exception of the platinum-group elements that generally show dramatic enhancements in the HgMn stars. Current theory and calculations are able to predict most observed abundances and abundance trends through the iron group. The large number of derived element abundances in this study provides a constraint for theoretical calculations attempting to explain the heavy element abundances in chemically peculiar stars. This paper includes a comprehensive description of spectral lines useful for an abundance analysis of late B and A type stars, and comments are provided on the atomic data. New data for hyperfine structure components for three lines in Lu iii and a single line in Lu ii are presented, based on laboratory spectra. In addition to the stellar spectrum, lines from the interstellar medium are noted for several of the strongest Fe ii ultraviolet transitions.

Probing the CGM of low-redshift dwarf galaxies using FIRE simulations

ABSTRACT Observations of ultraviolet (UV) metal absorption lines have provided insight into the structure and composition of the circumgalactic medium (CGM) around galaxies. We compare these observations with the low-redshift (z ≤ 0.3) CGM around dwarf galaxies in high-resolution cosmological zoom-in runs in the FIRE-2 (Feedback In Realistic Environments) simulation suite. We select simulated galaxies that match the halo mass, stellar mass, and redshift of the observed samples. We produce absorption measurements using trident for UV transitions of C iv, O vi, Mg ii, and Si iii. The FIRE equivalent width (EW) distributions and covering fractions for the C iv ion are broadly consistent with observations inside 0.5Rvir, but are underpredicted for O vi, Mg ii, and Si iii. The absorption strengths of the ions in the CGM are moderately correlated with the masses and star formation activity of the galaxies. The correlation strengths increase with the ionization potential of the ions. The structure and composition of the gas from the simulations exhibit three zones around dwarf galaxies characterized by distinct ion column densities: the discy interstellar medium, the inner CGM (the wind-dominated regime), and the outer CGM (the IGM accretion-dominated regime). We find that the outer CGM in the simulations is nearly but not quite supported by thermal pressure, so it is not in hydrostatic equilibrium, resulting in halo-scale bulk inflow and outflow motions. The net gas inflow rates are comparable to the star formation rate of the galaxy, but the bulk inflow and outflow rates are greater by an order of magnitude, with velocities comparable to the virial velocity of the halo. These roughly virial velocities (${\sim } 100 \, \rm km\, s^{-1}$) produce large EWs in the simulations. This supports a picture for dwarf galaxies in which the dynamics of the CGM at large scales are coupled to the small-scale star formation activity near the centre of their haloes.

Electron-rotation coupling in diatomics under strong-field excitation

The photoexcitation and photodissociation of diatomic molecules by intense pulse lasers has been the subject of extensive investigations over the past decades. However, the usually employed theoretical framework neglects the coupling between the molecular rotational angular momentum ($\mathbf{R}$) and the angular momentum of the electrons projected onto the molecular axis $\mathrm{\ensuremath{\Omega}}=\mathrm{\ensuremath{\Lambda}}+\mathrm{\ensuremath{\Sigma}}$, which results in the known $\mathrm{\ensuremath{\Lambda}}$-doubling phenomenon in high-resolution electronic spectra of diatomic molecules. While neglecting this coupling is an excellent approximation in the weak-field or perturbative regime owing to the large mass difference between the rotating atoms and the electrons, the approximation breaks down for intense laser pulses because of the repeated Rabi cycling of the electronic transitions, which can have a significant effect on the rotational degrees of freedom of the molecule. By correcting the transition dipole matrix elements and introducing angular basis sets based on Wigner D functions, the conventional theoretical treatment is generalized to a universal description valid for both the weak- and strong-field regimes. The theoretical treatment developed here is applied to the $|^{1}\mathrm{\ensuremath{\Sigma}}\ensuremath{\rangle}$ to $|^{1}\mathrm{\ensuremath{\Pi}}\ensuremath{\rangle}$ transitions in diatomic systems. Our results reveal that, for field intensities resulting in about one Rabi cycling for extreme ultraviolet or x-ray transitions, the theoretical predictions by the conventional theoretical frame need to be corrected when considering observables such as the molecular alignment and the angular distribution of the photofragments.