arXiv subjects

A. Borschevsky

Publications and source records attributed to A. Borschevsky.

30 records · Page 2Linked to original sources

arXiv2018

Energy Level Structure of Sn$^{3+}$ Ions

Laser-produced Sn plasma sources are used to generate extreme ultraviolet (EUV) light in state-of-the-art nanolithography. An ultraviolet and optical spectrum is measured from a droplet-based laser-produced Sn plasma, with a spectrograph covering the range 200 - 800 nm. This spectrum contains hundreds of spectral lines from lowly charged tin ions Sn$^{1+}$ - Sn$^{4+}$ of which a major fraction was hitherto unidentified. We present and identify a selected class of lines belonging to the quasi-one-electron, Ag-like ([Kr]$4d^{10} nl$ electronic configuration), Sn$^{3+}$ ion, linking the optical lines to a specific charge state by means of a masking technique. These line identifications are made with iterative guidance from COWAN code calculations. Of the 53 lines attributed to Sn$^{3+}$, some 20 were identified from previously known energy levels, and 33 lines are used to determine previously unknown level energies of 13 electronic configurations, i.e., $ 7p $, $ (7,8)d $, $ (5,6)f $, $ (6-8)g $, $ (6-8)h $, $ (7,8)i $. The consistency of the level energy determination is verified by the quantum-defect scaling procedure. The ionization limit of Sn$^{3+}$ is confirmed and refined to 328908.4 cm$^{-1}$ with an uncertainty of 2.1 cm$^{-1}$. The relativistic Fock space coupled cluster (FSCC) calculation of the measured level energies are generally in good agreement with experiment, but fail to reproduce the anomalous behavior of the $5d$ $^2$D and $nf$ $^2$F terms. By combining the strengths of FSCC, COWAN code calculations, and configuration interaction many-body perturbation theory (CI+MBPT), this behavior is shown to arise from interactions with doubly-excited configurations.

physics.atom-ph↗

arXiv2018

Enhanced nuclear spin dependent parity violation effects using the 199HgH molecule

Electron interactions with the nuclear-spin-dependent (NSD) parity non-conserving (PNC) anapole moment are strongly enhanced within heteronuclear diatomic molecules. A novel, low-energy optical rotation experiment is being proposed with the aim of observing NSD PNC interactions in HgH. Based on the relativistic coupled cluster method we present a complete calculation of the circular polarization parameter $P = 2\,\textrm{Im}(E1_{PNC})/M1 \approx 3 \times 10^{-6}\; κ$ for the $^2Σ_{1/2} \to ^2Π_{1/2}$ optical transition of HgH, where $κ$ is a dimensionless constant determined by the nuclear anapole moment. This provides an improvement in sensitivity to NSD PNC by 2 -- 3 orders of magnitude over the leading atomic Xe, Hg, Tl, Pb and Bi optical rotation experiments, and shows that the proposed measurement will be sensitive enough to extract the $^{199}$Hg anapole moment and shed light on the underlying theory of hadronic parity violation.

physics.atom-ph↗

arXiv2016

Analysis of the fine structure of Sn$^{11+...14+}$ ions by optical spectroscopy in an electron beam ion trap

We experimentally re-evaluate the fine structure of Sn$^{11+...14+}$ ions. These ions are essential in bright extreme-ultraviolet (EUV) plasma-light sources for next-generation nanolithography, but their complex electronic structure is an open challenge for both theory and experiment. We combine optical spectroscopy of magnetic dipole $M1$ transitions, in a wavelength range covering 260\,nm to 780\,nm, with charge-state selective ionization in an electron beam ion trap. Our measurements confirm the predictive power of \emph{ab initio} calculations based on Fock space coupled cluster theory. We validate our line identification using semi-empirical Cowan calculations with adjustable wavefunction parameters. Available Ritz combinations further strengthen our analysis. Comparison with previous work suggests that line identifications in the EUV need to be revisited.

physics.atom-ph↗

arXiv2015

Search for variation of fundamental constants: Strong enhancements in $X^2Π$ cations of dihalogens and hydrogen halides

We propose to use diatomic molecular ions to search for strongly enhanced effects of variation of fundamental constants. The relative enhancement occurs in transitions between nearly degenerate levels of different nature. Since the trapping techniques for molecular ions have already been developed, the molecules HBr$^+$, HI$^+$, Br$^+_2$, I$^+_2$, IBr$^+$, ICl$^+$, and IF$^+$ are very promising candidates for such future studies.

physics.chem-ph↗

arXiv2013

Relativistic study of the nuclear anapole moment effects in diatomic molecules

Nuclear-spin-dependent (NSD) parity violating effects are studied for a number of diatomic molecules using relativistic Hartree-Fock and density functional theory and accounting for core polarization effects. Heavy diatomic molecules are good candidates for the successful measurement of the nuclear anapole moment, which is the dominant NSD parity violation term in heavy elements. Improved results for the molecules studied in our previous publication [Borschevsky et al., Phys. Rev. A 85, 052509 (2012)] are presented along with the calculations for a number of new promising candidates for the nuclear anapole measurements.

physics.atom-ph↗

arXiv2012

Nuclear-spin dependent parity violation in diatomic molecular ions

Nuclear-spin-dependent (NSD) parity violating (PV) effects can be strongly enhanced in diatomic molecules containing heavy atoms. Future measurements are anticipated to provide nuclear anapole moments and strength constants for PV nuclear forces. In light molecules, the NSD electroweak electron-nucleus interaction may also be detected. Here we calculate NSD PV effects for molecular ions. Our calculations are motivated by rapid developments in trapping techniques for such systems at low temperatures.

physics.atom-ph↗

arXiv2012

Relativistic ab initio calculations of the P-odd interaction constant W_A in diatomic molecules

We present ab initio calculations of the $W_A$ parameter of the P-odd spin-rotational Hamiltonian for a variety of diatomic molecules, including the group--2 and --12 halides. The results were obtained by relativistic Dirac--Hartree--Fock and density functional theory approaches, and corrected for core polarization effects. Strong enhancement of $W_A$ is found for the group--12 diatomic halides, which should be helpful in future determination of the nuclear anapole moment.

physics.atom-ph↗

arXiv2011

Effect of alpha variation on the vibrational spectrum of Sr_2

We consider the effect of $α$ variation on the vibrational spectrum of Sr$_2$ in the context of a planned experiment to test the stability of $μ\equiv m_e/m_p$ using optically trapped Sr$_2$ molecules [Zelevinsky et al., Phys. Rev. Lett. {\bf 100}, 043201; Kotochigova et al., Phys. Rev. A {\bf 79}, 012504]. We find the prospective experiment to be 3 to 4 times less sensitive to fractional variation in $α$ as it is to fractional variation in $μ$. Depending on the precision ultimately achieved by the experiment, this result may give justification for the neglect of $α$ variation or, alternatively, may call for its explicit consideration in the interpretation of experimental results.

physics.atom-ph↗

arXiv2011

Effect of alpha variation on a prospective experiment to detect variation of m_e/m_p in diatomic molecules

We consider the influence of variation in the fine structure constant alpha on a promising experiment proposed by DeMille et al. to search for variation in the electron-to-proton mass ratio mu using diatomic molecules [DeMille et al., Phys. Rev. Lett. 100, 043202 (2008)]. The proposed experiment involves spectroscopically probing the splitting between two nearly-degenerate vibrational levels supported by different electronic potentials. Here we demonstrate that this splitting may be equally or more sensitive to variation in alpha as to variation in mu. For the anticipated experimental precision, this implies that the alpha variation may not be negligible, as previously assumed, and further suggests that the method could serve as a competitive means to search for alpha variation as well.

physics.atom-ph↗

arXiv2011

Rotational spectrum of molecular ion NH^+ as a probe for alpha- and m_e/m_p-variation

We identify the molecular ion NH^+ as a potential candidate for probing variations in the fine structure constant alpha and electron-to-proton mass ratio mu. NH^+ has an anomalously low-lying excited Sigma state, being only a few hundred cm^-1 above the ground Pi state. Being a light molecule, this proximity is such that rotational levels of the respective states are highly intermixed for low angular momenta. We find that several low-frequency transitions within the collective rotational spectrum experience enhanced sensitivity to alpha- and mu-variation. This is attributable to the close proximity of the Pi and Sigma states, as well as the ensuing strong spin-orbit coupling between them. Suggestions that NH^+ may exist in interstellar space and recent predictions that trapped-ion precision spectroscopy will be adaptable to molecular ions make NH^+ a promising system for future astrophysical and laboratory studies of alpha- and mu-variation.

physics.atom-ph↗

arXiv2011

Sensitivity to alpha-variation in ultracold atomic-scattering experiments

We present numerical calculations for cesium and mercury to estimate the sensitivity of the scattering length to the variation of the fine structure constant alpha. The method used follows ideas Chin and Flambaum [Phys. Rev. Lett. 96, 230801 (2006)], where the sensitivity to the variation of the electron to proton mass ratio, beta, was considered. We demonstrate that for heavy systems, the sensitivity to variation of alpha is of the same order of magnitude as to variation of beta. Near narrow Feshbach resonances the enhancement of the sensitivity may exceed nine orders of magnitude.

physics.atom-ph↗

arXiv2010

Enhanced Sensitivity to the Time Variation of the Fine-Structure Constant and $m_p/m_e$ in Diatomic Molecules: A Closer Examination of Silicon Monobromide

Recently it was pointed out that transition frequencies in certain diatomic molecules have an enhanced sensitivity to variations in the fine-structure constant $α$ and the proton-to-electron mass ratio $m_p/m_e$ due to a near cancellation between the fine-structure and vibrational interval in a ground electronic multiplet [V.~V.~Flambaum and M.~G.~Kozlov, Phys. Rev. Lett.~{\bf 99}, 150801 (2007)]. One such molecule possessing this favorable quality is silicon monobromide. Here we take a closer examination of SiBr as a candidate for detecting variations in $α$ and $m_p/m_e$. We analyze the rovibronic spectrum by employing the most accurate experimental data available in the literature and perform \emph{ab initio} calculations to determine the precise dependence of the spectrum on variations in $α$. Furthermore, we calculate the natural linewidths of the rovibronic levels, which place a fundamental limit on the accuracy to which variations may be determined.

physics.atom-ph↗