Resonance Ionization Spectroscopy Research Articles

A resonant ionization spectroscopy scheme for photodetachment studies

SynopsisA refined Resonant Ionization Spectroscopy (RIS) scheme for high resolution Laser Photodetachment Threshold Spectroscopy (LPTS). In this work the scheme is used to measure the electron affinity of cesium.

Development of an interference-filter-type external-cavity diode laser for resonance ionization spectroscopy of strontium.

A frequency tunable external-cavity diode laser (ECDL) using a narrow bandwidth (∼0.3 nm) interference filter has been developed for resonance ionization spectroscopy of strontium (Sr) with high isotopic selectivity. Improved wavelength and single mode stabilities of this interference-filter-type ECDL (IF-ECDL) over a commonly used (also home-made) Littrow-type ECDL were theoretically expected and experimentally confirmed by both a wavelength meter and a home-made Fabry-Perot interferometer. The measured spectral profile of the dominant isotope 88Sr using our IF-ECDL in the 689.4 nm intercombination transition shows that the Lorentzian component (∼1.3 MHz) of the spectrum width is consistent with the obtained fringe width of the interferometer. High 90Sr isotopic selectivity of ∼104 with respect to 88Sr is expected in this transition, which indicates that even if the manufacturing accuracy is not comparable to commercial Littrow-type ECDLs, our compact IF-ECDL having sufficient wavelength stability is a promising laser source for background-free analysis of radioactive 90Sr in marine samples.

Rydberg and autoionizing states of tellurium studied by laser resonance ionization spectroscopy

Multistep laser-resonance-ionization spectroscopy of tellurium (Te) has been performed at TRIUMF's off-line laser ion source test stand. Six clean and regular even-parity Rydberg series $5{p}^{3}$ $({^{4}S}_{3/2}^{\ensuremath{\circ}})$ $np\phantom{\rule{4pt}{0ex}}^{3}P_{0,1,2}$, $np\phantom{\rule{4pt}{0ex}}^{5}P_{1,2}$, and $nf\phantom{\rule{4pt}{0ex}}^{3}F_{2}/^{5}F_{1,2}$ were observed. The ionization potential of Te was extracted from the measured series as $72669.114{(56)}_{\mathrm{stat}}{(45)}_{\mathrm{sys}}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. Excited from two different intermediate levels, seven odd-parity autoionization Rydberg series converging to the $5{s}^{2}5{p}^{3}$ $({^{2}D}_{3/2}^{\ensuremath{\circ}})$ core state of Te were obtained.

High efficiency resonance ionization of thorium

Multi-step resonance ionization spectroscopy of thorium has been performed with Ti:Sapphire lasers and a hot-cavity laser ion source. Resonance ionization schemes involving three-color, three-photon ionization processes are evaluated and a new three-photon scheme is demonstrated with measured overall ionization efficiency of 38.6(5)%. This high efficiency makes it possible to determine the thorium impurities in materials used for ultra-low background neutrino detectors and could also benefit ultra-trace thorium analysis using resonance ionization mass spectrometry for various radiochemical tracer applications.

Trace analysis of radioisotopes by laser spectroscopy and mass spectrometry

Trace analysis (at fg-level) of radioisotopes requires a considerable push in analytical technology. Among most sensitive are a Time-Resolved Laser-Induced Fluorescence (TRLIF) and Chemiluminescence (TRLIC) methods for detection of elemental compositions and valence states and a Resonance Ionisation Spectroscopy (RIS) in combination with mass spectrometry for isotope composition determination. The radioisotopes of interest in environmental radiochemistry and planetary science and their analysis using TRLIF/TRLIC/RIS are discussed. The aspects of the development of the new technology implementing these methods are also described.

Search for octupole-deformed actinium isotopes using resonance ionization spectroscopy

In-source resonance ionization spectroscopy of the neutron-rich actinium isotopes $^{225\ensuremath{-}229}\mathrm{Ac}$ has been performed at the ISAC facility in TRIUMF, probing a $^{2}D_{3/2}\ensuremath{\rightarrow}^{4}P_{5/2}^{\ensuremath{\circ}}$ atomic transition. New data on the magnetic dipole moments and changes in mean-square charge radii $\ensuremath{\delta}\ensuremath{\langle}{r}^{2}\ensuremath{\rangle}$ of $^{226,228,229}\mathrm{Ac}$ have been obtained. The comparison of the measured isotope shifts and magnetic dipole coupling constants $a(^{4}P_{5/2}^{\ensuremath{\circ}})$ of $^{225,227}\mathrm{Ac}$ with a high-resolution data set is used to identify systematic uncertainties on the deduced $\ensuremath{\delta}{\ensuremath{\langle}{r}^{2}\ensuremath{\rangle}}^{A,215}$ and magnetic dipole moment values. The charge radii odd-even staggering is evaluated for the odd-$N$ isotopes, showing that $^{226}\mathrm{Ac}$ has an inverted odd-even staggering that might be linked with a reflection-asymmetric shape. Comparison of the magnetic dipole moments of $^{225,227,229}\mathrm{Ac}$ with Nilsson-model estimates supports the assumption of octupole deformation in isotopes $^{225,227}\mathrm{Ac}$ and its gradual decrease toward isotope $^{229}\mathrm{Ac}$. The changes in mean-square charge radii are compared to self-consistent calculations employing multiple modern energy density functionals: SLy5s1, BSk31, and DD-MEB1. For SLy5s1 in particular, self-consistent time-reversal breaking calculations of odd-odd nuclei incorporating finite octupole deformation are reported for the first time. For these calculations, the overall best agreement is obtained when the octupole degree of freedom is taken into account.

Conformer Specific Ultraviolet and Infrared Detection of Nicotine in the Vapor Phase.

A gas-phase electronic spectrum of nicotine in a supersonic expansion has been recorded using two-color resonant two-photon ionization spectroscopy. Efficient photoionization was achievable only via the pyridine chromophore owing to poor Franck-Condon overlap in the N-methylpyrrolidine moiety. Two conformers of nicotine have been characterized and assigned by infrared-ultraviolet (IR-UV) ion depletion and IR-UV hole-burning spectroscopy, in combination with quantum chemical techniques. Trans-A with nitrogen atoms further apart is more stable by 2 kJ mol-1 and the most populated conformer in the supersonic jet, owing this stability to a stronger inter-ring CH···N hydrogen bond than the trans-B counterpart.

Investigation of high-lying even-parity levels of atomic samarium with multi-color photoionization technique: Energies and radiative lifetimes

We have investigated high-lying even-parity energy levels of atomic samarium in the energy region 32,156.3–32,886.4 cm−1 using two-color three-step photoionization technique. The experiments have been carried out in an atomic beam coupled to a linear time of flight mass spectrometer. The analysis of the photoionization spectra has resulted in the identification of twenty-five high-lying even-parity energy levels of atomic samarium. These include the confirmation of fifteen energy levels reported earlier while the remaining ten energy levels are new. The observed relative photoionization signal intensities of the corresponding transitions are also reported. The possible total angular momenta of the newly discovered energy levels have been assigned by the total angular momentum selection rules. Further, the radiative lifetimes of twenty high-lying even-parity energy levels of atomic samarium were measured for the first time by delayed three-color three-photon resonance ionization spectroscopy via a pump-probe method.

Precision measurements of the charge radii of potassium isotopes

Precision nuclear charge radii measurements in the light-mass region are essential for understanding the evolution of nuclear structure, but their measurement represents a great challenge for experimental techniques. At the Collinear Resonance Ionization Spectroscopy (CRIS) setup at ISOLDE-CERN, a laser frequency calibration and monitoring system was installed and commissioned through the hyperfine spectra measurement of $^{38--47}\mathrm{K}$. It allowed for the extraction of the hyperfine parameters and isotope shifts with better than 1 MHz precision. These results are in excellent agreement with available literature values and they demonstrate the suitability of the CRIS technique for the study of nuclear observables in light atomic systems. In addition, the spectral line shapes obtained under different conditions were systematically investigated, highlighting the importance of finding optimal conditions, under which the extracted nuclear properties remain unaffected by laser-atom interactions.

Bond dissociation energies of FeB, CoB, NiB, RuB, RhB, OsB, IrB, and PtB.

The bond dissociation energies (BDEs) of the diatomic late transition metal borides (MB, M = Fe, Co, Ni, Ru, Rh, Os, Ir, and Pt) have been assigned from the measurement of a predissociation threshold using resonant two-photon ionization (R2PI) spectroscopy. The open d-shell configurations of the transition metal constituents in the molecules studied here lead to large ML degeneracies, resulting in a dense manifold of states near the ground separated atom limit. This high density of states causes prompt predissociation to occur as soon as the ground separated atom limit is exceeded, allowing a precise assignment of the BDE of the molecule. The measured predissociation thresholds give BDEs of D0(FeB) = 2.43(2) eV, D0(CoB) = 2.954(3) eV, D0(NiB) = 3.431(4) eV, D0(RuB) = 4.815(3) eV, D0(RhB) = 5.252(3) eV, D0(OsB) = 4.378(3) eV, D0(IrB) = 4.928(10) eV, and D0(PtB) = 5.235(3) eV. The gaseous enthalpies of formation at 0 K for these molecules have been derived using a thermochemical cycle that relates atomic enthalpies of formation and the BDE of the molecule, giving ΔfH0K°(g) (FeB) = 733.6(12.2) kJ mol-1, ΔfH0K°(g) (CoB) = 695.1(12.2) kJ mol-1, ΔfH0K°(g) (NiB) = 652.1(14.7) kJ mol-1, ΔfH0K°(g) (RuB) = 740.2(12.7) kJ mol-1, ΔfH0K°(g) (RhB) = 600.1(12.7) kJ mol-1, ΔfH0K°(g) (OsB) = 921.7(13.6) kJ mol-1, ΔfH0K°(g) (IrB) = 748.0(13.6) kJ mol-1, and ΔfH0K°(g) (PtB) = 613.9(12.2) kJ mol-1. This work reports the first experimental measurements of the BDEs of FeB, CoB, NiB, and OsB. Periodic trends are discussed.

Cation spectra of p-chloroanisole and the heavy atom effect on ionization energy

Vibrationally resolved cation spectra of p-chloroanisole were recorded by ionizing via four vibronic levels through two-color resonant two-photon mass-analyzed threshold ionization (MATI) spectroscopy techniques. The results indicated that the geometry and molecular vibrations 7a, 16b, and 6a of p-chloroanisole in the cationic ground D0 state resemble those in the electronically excited neutral S1 state. The precisely measured adiabatic ionization energy of this molecule was less than that of p-fluoroanisole by 325 cm−1. This can be labeled as a heavy atom effect, which is similar to that observed for para halogen-substituted phenol and aniline.

Bond dissociation energies of ScSi, YSi, LaSi, ScC, YC, LaC, CoC, and YCH.

Predissociation thresholds of the ScSi, YSi, LaSi, ScC, YC, LaC, CoC, and YCH molecules have been measured using resonant two-photon ionization spectroscopy. It is argued that the dense manifold of electronic states present in these molecules causes prompt dissociation when the bond dissociation energy (BDE) is exceeded, allowing their respective predissociation thresholds to provide precise values of their bond energies. The BDEs were measured as 2.015(3) eV (ScSi), 2.450(2) eV (YSi), 2.891(5) eV (LaSi), 3.042(10) eV (ScC), 3.420(3) eV (YC), 4.718(4) eV (LaC), 3.899(13) eV (CoC), and 4.102(3) eV (Y-CH). Using thermochemical cycles, the enthalpies of formation, ΔfH0K°(g), were calculated as 627.4(9.0) kJ mol-1 (ScSi), 633.1(9.0) kJ mol-1 (YSi), 598.1(9.0) kJ mol-1 (LaSi), 793.8(4.3) kJ mol-1 (ScC), 805.0(4.2) kJ mol-1 (YC), 687.3(4.2) kJ mol-1 (LaC), 760.1(2.5) kJ mol-1 (CoC), and 620.8(4.2) kJ mol-1 (YCH). Using data for the BDEs of the corresponding cations allows ionization energies to be obtained through thermochemical cycles as 6.07(11) eV (ScSi), 6.15(13) eV (YSi), 5.60(10) eV (LaSi), 6.26(6) eV (ScC), 6.73(12) or 5.72(11) eV [YC, depending on the value of D0(Y+-C) employed], and 5.88(35) eV (LaC). Additionally, a new value of D0(Co+-C) = 4.045(13) eV was obtained based on the present work and the previously determined ionization energy of CoC. An ionization onset threshold allowed the measurement of the LaSi ionization energy as 5.607(10) eV, in excellent agreement with a prediction based on a thermochemical cycle. Chemical bonding trends are also discussed.

Atomic transitions and the first ionization potential of promethium determined by laser spectroscopy

The atomic spectrum of neutral promethium has been studied extensively by laser resonance ionization spectroscopy. We report on more than 1000 atomic transitions in the blue and near infrared spectral ranges, most of them between high excited energy levels. As Rydberg convergences could not be assigned unambiguously in the dense spectrum at high excitation energies, the first ionization potential (IP) was determined via field ionization of weakly bound states within a static electric field. By applying the saddle-point model, a value of ${\mathrm{IP}}_{(\mathrm{Pm})}=45\phantom{\rule{0.16em}{0ex}}020.8(3)\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1} [5.58188(4)\phantom{\rule{0.16em}{0ex}}\mathrm{eV}]$ was derived, which confirms previous expectations of $45\phantom{\rule{0.16em}{0ex}}027(80)$ and $44\phantom{\rule{0.16em}{0ex}}985(140)\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, which were obtained indirectly from lanthanide IP systematics.

Cation Vibrations of 1-Methylnaphthalene and 2-Methylnaphthalene through Mass-Analyzed Threshold Ionization Spectroscopy.

Vibrationally resolved cation spectra of 1-methylnaphthalene (1MN) and 2-methylnaphthalene (2MN) were obtained using the two-color resonant two-photon mass-analyzed threshold ionization (MATI) spectroscopy. MATI spectra were obtained through ionization via several intermediate vibronic levels. Due to hindrance effect, no spectral features related to methyl torsion were observed in the MATI spectra of 1MN. By contrast, most of the in-plane ring deformation vibrations of the 2MN cation were found to couple with methyl torsion because of its small internal rotational barrier. These experimental findings were well supported by our theoretical calculations.

A direct diode pumped continuous-wave Ti:sapphire laser as seed of a pulsed amplifier for high-resolution resonance ionization spectroscopy

Progress of the development of a tunable continuous-wave directly diode-pumped Ti:sapphire laser is reported. The pump diode system based on InGaN multimode emitters in the blue-green wavelength region is characterized in terms of beam quality and output power. A prototype bow-tie resonator with a short highly doped Brewster-cut Ti:sapphire crystal was investigated. Output power scaling with the number of pump diodes and output coupling ratio as well as wavelength tuning range using a three-plate birefringent filter was measured.

Inverse odd-even staggering in nuclear charge radii and possible octupole collectivity in At217,218,219 revealed by in-source laser spectroscopy

Hyperfine-structure parameters and isotope shifts for the 795-nm atomic transitions in $^{217,218,219}$At have been measured at CERN-ISOLDE, using the in-source resonance-ionization spectroscopy technique. Magnetic dipole and electric quadrupole moments, and changes in the nuclear mean-square charge radii, have been deduced. A large inverse odd-even staggering in radii, which may be associated with the presence of octupole collectivity, has been observed. Namely, the radius of the odd-odd isotope $^{218}$At has been found to be larger than the average of its even-$N$ neighbors, $^{217,219}$At. The discrepancy between the additivity-rule prediction and experimental data for the magnetic moment of $^{218}$At also supports the possible presence of octupole collectivity in the considered nuclei.

A compact RFQ cooler buncher for CRIS experiments

A compact radio frequency cooler buncher (RFQCB) is currently in development between The University of Manchester, KU Leuven, and CERN. The device will be installed as part of the Collinear Resonance Ionisation Spectroscopy (CRIS) experiment at the Isotope separator On-line device (ISOLDE) at CERN. The purpose of developing a dedicated RFQCB for the CRIS experiment is to increase data collection efficiency, and simplify the process of obtaining reference measurements with stable isotopes. The CRIS technique is outlined in addition to an overview of the proposed RFQCB, and its potential compatibility for implementation at ISOLDE.

A compact linear Paul trap cooler buncher for CRIS

A gas-filled linear Paul trap for the Collinear Resonance Ionisation Spectroscopy (CRIS) experiment at ISOLDE, CERN is currently under development. The trap is designed to accept beam from both ISOLDE target stations and the CRIS stable ion source. The motivation for the project along with the current design, simulations and future plans, will be outlined.

Resonance ionization schemes for high resolution and high efficiency studies of exotic nuclei at the CRIS experiment

This paper presents an overview of recent resonance ionization schemes used at the Collinear Resonance Ionization Spectroscopy (CRIS) setup located at ISOLDE, CERN. The developments needed to reach high spectral resolution and efficiency will be discussed. Besides laser ionization efficiency and high resolving power, experiments on rare isotopes also require low-background conditions. Ongoing developments that aim to deal with beam-related sources of background are presented.

Shape staggering of midshell mercury isotopes from in-source laser spectroscopy compared with density-functional-theory and Monte Carlo shell-model calculations

Neutron-deficient $^{177-185}$Hg isotopes were studied using in-source laser resonance-ionization spectroscopy at the CERN-ISOLDE radioactive ion-beam facility, in an experiment combining different detection methods tailored to the studied isotopes. These include either alpha-decay tagging or Multi-reflection Time-of-Flight gating to identify the isotopes of interest. The endpoint of the odd-even nuclear shape staggering in mercury was observed directly by measuring for the first time the isotope shifts and hyperfine structures of $^{177-180}$Hg. Changes in the mean-square charge radii for all mentioned isotopes, magnetic dipole and electric quadrupole moments of the odd-A isotopes and arguments in favor of $I = 7/2$ spin assignment for $^{177,179}$Hg were deduced. Experimental results are compared with Density Functional Theory (DFT) and Monte-Carlo Shell Model (MCSM) calculations. DFT calculations with several Skyrme parameterizations predict a large jump in the charge radius around the neutron $N = 104$ mid shell, with an odd-even staggering pattern related to the coexistence of nearly-degenerate oblate and prolate minima. This near-degeneracy is highly sensitive to many aspects of the effective interaction, a fact that renders perfect agreement with experiment out of reach for current functionals. Despite this inherent diffculty, the SLy5s1 and a modified UNEDF1^{SO} parameterization predict a qualitatively correct staggering that is off by two neutron numbers. MCSM calculations of states with the experimental spins and parities show good agreement for both electromagnetic moments and the observed charge radii. A clear mechanism for the origin of shape staggering within this context is identified: a substantial change in occupancy of the proton $\pi h_{9/2}$ and neutron $\nu i_{13/2}$ orbitals.