Resonance Ionization Spectroscopy Research Articles

Rotamers of 3,4-difluorophenol studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy

Abstract We applied the resonant two-photon ionization and mass-analyzed threshold ionization techniques to record the vibrational spectra of 3,4-difluorophenol in the first electronically excited and the ionic ground states. The band origins of the S1 ← S0 electronic transition of the cis and trans rotamers are found to be 35,486 ± 2 and 35,704 ± 2 cm−1 and the adiabatic ionization energies are 70,016 ± 5 and 70,203 ± 5 cm−1, respectively. The distinct spectral features mainly result from the in-plane ring deformation and substituent-sensitive bending vibrations. Spectral analysis suggests that the molecular geometry and vibrational coordinates of the cation in the D0 state resemble those of the neutral species in the S1 state for both cis and trans rotamers.

Properties of Fr-like Th3+from rf spectroscopy of high-LTh2+Rydberg ions

Relative positions of twenty $n=28$ Rydberg levels of Th${}^{2+}$ with $L=9$, 10, 11, and 12 were determined with sub-MHz precision using the rf-RESIS (resonant excitation Stark ionization spectroscopy) technique. The pattern of binding energies was analyzed with the effective potential model, modified to account for significant nonadiabatic effects. The analysis yielded measurements of several properties of the Fr-like Th${}^{3+}$ core ion, including the quadrupole moment, $Q=0.5931$(14) a.u.; hexadecapole moment, \ensuremath{\Pi} $=$ \ensuremath{-}0.69(28) a.u.; $g$ factor, ${g}_{J}=1.24$(48); scalar and tensor dipole polarizabilities, \ensuremath{\alpha}${}_{D}$${}_{,0}=15.224$(33) a.u. and \ensuremath{\alpha}${}_{D}$${}_{,2}$ $=$ \ensuremath{-}5.30(11) a.u.; scalar quadrupole polarizability, \ensuremath{\alpha}${}_{Q}$${}_{,0}=60$(15) a.u.; and the reduced dipole and octupole matrix elements connecting the ground 5$f$ ${}^{2}$${F}_{5/2}$ level with the low-lying 6$d$ ${}^{2}$${D}_{3/2}$ level, $|{\ensuremath{\langle}}^{2}{F}_{5/2}||{\mathrm{M}}^{[1]}|{|}^{2}{D}_{3/2}\ensuremath{\rangle}|=1.436(2)$ a.u. and $|{\ensuremath{\langle}}^{2}{F}_{5/2}||{\mathrm{M}}^{[3]}|{|}^{2}{D}_{3/2}\ensuremath{\rangle}|=3.3(1.1)$ a.u. The measured properties are compared with theoretical predictions.

Electronic Spectroscopy of Diatomic VC

Resonant two-photon ionization spectroscopy has been applied to diatomic VC, providing the first optical spectrum of this molecule. The ground state is determined to be a (2)Δ3/2 state that arises from the 1σ(2)1π(4)2σ(2)1δ(1) configuration. The r0" ground-state bond length is 1.6167(3) Å. The manifold of excited vibronic states in the visible portion of the spectrum is quite dense, but two possible vibrational progressions have been identified. It is noted that VC joins CrC, NbC, and MoC as species in which the metal ns-based 3σ orbital is unoccupied, resulting in large dipole moments in the ground states of these molecules. In the corresponding 5d metal carbides, however, the 3σ orbital is occupied, leading to different ground electronic states of the 5d congeners, TaC and WC.

Development of resonance ionization in a supersonic gas-jet for studies of short-lived and long-lived radioactive nuclei

High-resolution resonance ionization spectroscopy (RIS) is required for laser spectroscopy and trace analysis of short-lived and long-lived radioactive nuclei. We have proposed high-resolution resonance ionization spectroscopy in a gas jet combined with a narrow band-width injection-locked Ti:Sapphire laser. Resonance ionization of stable 93Nb in a gas jet was demonstrated using a broad bandwidth Ti:Sapphire laser. In addition, a setup for high-resolution RIS in a gas-jet was designed using numerical simulations of the gas-jet conditions based on computational fluid dynamics.

Resonant Ionization Laser Ion Source (RILIS) off-line developments on Ga, Al and Ca

The Resonant Ionization Laser Ion Source (RILIS) is an element selective, highly efficient and versatile tool for generation of radioactive ion beams at on-line mass separator facilities. Parallel to TRIUMF’s on-line RILIS at the Isotope Separator and ACcelerator (ISAC) facility, an off-line Laser Ion Source test stand (LIS STAND) is operated for systematic laser resonance ionization spectroscopy, ionization scheme and ion source development. Three titanium sapphire (Ti:Sa) lasers optionally equipped with harmonic frequency generation units are used to resonantly step-wise excite and ionize elements of interest. A grating tuned Ti:Sa laser allows continuous laser wavelength scans of up to Δ≈200nm. With this laser inventory and the LIS STAND, atomic Rydberg series and auto-ionizing levels can systematically be studied. The LIS STAND has been in use since 2009 and so far the spectroscopy on Ga, Al and Ca has been performed. The development of efficient laser resonant ionization schemes, their investigation and comparison using the LIS STAND are discussed.

Excited-State Structure and Dynamics of Keto–Amino Cytosine: The 1ππ* State Is Nonplanar and Its Radiationless Decay Is Not Ultrafast

We have measured the mass- and tautomer-specific S0 → S1 vibronic spectra and S1 state lifetimes of the keto–amino tautomer of cytosine cooled in supersonic jets, using two-color resonant two-photon ionization (R2PI) spectroscopy at 0.05 cm(–1) resolution. The rotational contours of the 0(0)(0) band and nine vibronic bands up to +437 cm(–1) are polarized in the pyrimidinone plane, proving that the electronic excitation is to a 1ππ* state. All vibronic excitations up to +437 cm(–1) are overtone and combination bands of the low-frequency out-of-plane ν1′ (butterfly), ν2′ (boat), and ν3′ (H–N–C6–H twist) vibrations. UV vibronic spectrum simulations based on approximate second-order coupled-cluster (CC2) calculations of the ground and 1ππ* states are in good agreement with the experimental R2PI spectrum, but only if the calculated ν1′ and ν2′ frequencies are reduced by a factor of 4 and anharmonicity is included. Together with the high intensity of the ν1′ and ν2′ overtone vibronic excitations, this implies that the 1ππ* potential energy surface is much softer and much more anharmonic in the out-of-plane directions than predicted by the CC2 method. The 1ππ* state lifetime is determined from the Lorentzian line broadening necessary to reproduce the rotational band contours: at the 0(0)(0) band it is τ = 44 ps, remains at τ = 35–45 ps up to +205 cm(–1), and decreases to 25–30 ps up to +437 cm(–1). These lifetimes are 20–40 times longer than the 0.5–1.5 ps lifetimes previously measured with femtosecond pump–probe techniques at higher vibrational energies (1500–3800 cm(–1)). Thus, the nonradiative relaxation rate of keto–amino cytosine close to the 1ππ* state minimum is k(nr) 2.5 × 10(10) s(–1), much smaller than at higher energies. An additional nonradiative decay channel opens at +500 cm(–1) excess energy. Since high overtone bands of ν1′ and ν2′ are observed in the R2PI spectrum but only a single weak 2ν3′ band, we propose that ν3′ is a promoting mode for nonradiative decay, consistent with the observation that the ν3′ normal-mode eigenvector points toward the “C6-puckered” conical intersection geometry.

Resonant two-photon ionization spectroscopy of jet-cooled UN: Determination of the ground state

The optical transitions of supersonically cooled uranium nitride (UN) have been investigated in the range from 19,200 to 23,900 cm(-1) using resonant two-photon ionization spectroscopy. A large number of bands have been observed, of which seven have been rotationally resolved and analyzed. All are found to arise from the same state, which is presumably the ground state of the molecule. From the analysis of the bands, the ground state has Ω = 3.5, with a bond length of 1.7650(12) Å. Comparisons to the known isovalent molecules are made, and the variations in ground state configuration are explained in terms of the configurational reordering that occurs with changes in the nuclear and ligand charges. It is concluded that the UN molecule is best considered as a U(3+)N(3-) species in which the closed shell nitride ligand interacts with a U(3+) ion. The ground state of the molecule derives from a U(3+) ion in its 7s(1)5f 2) atomic configuration.

Electronic spectroscopy and electronic structure of diatomic IrSi

The optical spectrum of diatomic IrSi has been investigated for the first time, with transitions observed in the range from 17,178 to 23,858 cm(-1) (582-419 nm). A rich spectrum has been recorded, consisting of 14 electronic band systems and a number of unclassified bands. Thirty-one bands have been investigated with rotational resolution, allowing the ground state to be identified as X(2)Δ5∕2 arising from the 1σ(2)1π(4)2σ(2)1δ(3)3σ(2) configuration. The ground X(2)Δ5∕2 state is characterized by ΔG1∕2 = 533 cm(-1) and r0 = 2.0899(1) Å for the more abundant isotopic form, (193)Ir(28)Si (57.8%). The measured excited electronic states have equilibrium bond lengths ranging from 2.17 to 2.25 Å and vibrational frequencies ranging from 365 to 452 cm(-1). Ab initio calculations were also carried out on the molecule using the complete active space self-consistent field and multistate complete active space second-order perturbation theory methods, with relativistic and spin-orbit effects included through the restricted active space state-interaction with spin-orbit coupling method. The calculated ground state agrees with experiment, and a large number of excited states lying within 20,000 cm(-1) of the ground state are reported.

Electronic Spectroscopy and Electronic Structure of Copper Acetylide, CuCCH

The optical spectrum of the linear CuCCH molecule has been investigated for the first time, using resonant two-photon ionization spectroscopy employing ArF (193 nm) or F2 (157 nm) excimer radiation for photoionization. Scans over the range 19 400-25 200 cm(-1) were conducted, leading to the observation of three electronic band systems. These are identified as the [20.2] ã1 ← X̃ (1)Σ(+), the [23.1] à (1)Σ(+) ← X̃ (1)Σ(+), and the [24.7] B̃ (1)Π ← X̃ (1)Σ(+) systems, although only the first two have been rotationally resolved. The ã1 state is tentatively assigned as having (3)Π1 symmetry, becoming optically accessible through spin-orbit interaction with the B̃ (1)Π state. Vibrational assignments have provided the frequency of the Cu-C stretching mode, ν3, in the ground and all three excited states, along with both bending modes, ν4 and ν5, in the à (1)Σ(+) and B̃ (1)Π states, and the Cu-C≡C bending mode, ν5, in the ground state. Comparisons are made to the known electronic states of CuF, CuCl, CuBr, and CuI, and it is argued that like these molecules, the CuCCH molecule is essentially ionic in both the ground and excited states, with the ground state correlating diabatically to Cu(+) (3d(10), (1)S) + CCH(-) (X̃ (1)Σ(+)) and the excited states correlating diabatically to Cu(+) (3d(9)4s(1), (1,3)D) + CCH(-) (X̃ (1)Σ(+)).

First on-line results from the CRIS (Collinear Resonant Ionisation Spectroscopy) beam line at ISOLDE

The CRIS (Collinear Resonant Ionisation Spectroscopy) experiment at the on-line isotope separator facility, ISOLDE, CERN, has been constructed for high-sensitivity laser spectroscopy measurements on radioactive isotopes. The technique determines the magnetic dipole and electric quadrupole moments, nuclear spin and changes in mean-square charge radii of exotic nuclei via measurement of their hyperfine structures and isotope shifts. In November 2011 the first on-line run was performed using the CRIS beam line, when the hyperfine structure of 207Fr was successfully measured. This paper will describe the technique and experimental setup of CRIS and present the results from the first on-line experiment.

Development of high resolution resonance ionization mass spectrometry for trace analysis of 93mNb

93Nb(n, n′)93mNb reaction allows retrospective estimation of integrated fast neutron dose in nuclear reactor. We proposed isomer-selective trace analysis of 93mNb by Resonance Ionization Mass Spectrometry (RIMS) combined with a gas-jet atomic source and an injection locked Ti:Sapphire laser system operated at several kHz. Resonant ionization spectroscopy of Nb in gas-jet using Ti:Sapphire laser was demonstrated.

Laser assisted decay spectroscopy at the CRIS beam line at ISOLDE

The new collinear resonant ionization spectroscopy (Cris) experiment at Isolde, Cern uses laser radiation to stepwise excite and ionize an atomic beam for the purpose of ultra-sensitive detection of rare isotopes and hyperfine structure measurements. The technique also offers the ability to purify an ion beam that is contaminated with radioactive isobars, including the ground state of an isotope from its isomer. A new program using the Cris technique to select only nuclear isomeric states for decay spectroscopy commenced last year. The isomeric ion beam is selected using a resonance within its hyperfine structure and subsequently deflected to a decay spectroscopy station. This consists of a rotating wheel implantation system for alpha and beta decay spectroscopy, and up to three high purity germanium detectors for gamma-ray detection. This paper gives an introduction to the Cris technique, the current status of the laser assisted decay spectroscopy set-up and recent results from the experiment in November 2011.

Charge radii of odd-A191–211Po isotopes

Isotope shifts have been measured for the odd-A polonium isotopes 191–211Po and changes in the nuclear mean square charge radii δ〈r2〉 have been deduced. The measurements were performed at CERN-ISOLDE using the in-source resonance-ionization spectroscopy technique. The combined analysis of these data and our recent results for even-A polonium isotopes indicates an onset of deformation already at 197,198Po, when going away from stability. This is significantly earlier than was suggested by previous theoretical and experimental studies of the polonium isotopes. Moreover and in contrast to the mercury isotopes, where a strong odd–even staggering of the charge radii of the ground states was observed by approaching the neutron mid-shell at N=104, no such effect is present in polonium down to 191Po. Consequently the charge radii of both isomeric and ground states of the odd-A polonium isotopes follow the same trend as the even-A isotopes.

A test stand for off-line laser ion source development at TRIUMF

A test stand for ion source development and laser resonance ionization spectroscopy was built and commissioned at TRIUMF. The test stand is needed to develop efficient ion sources that can function reliably in the hostile, high temperature, high radiation environment of TRIUMF's isotope separator on-line (ISOL) production target ion source. In addition, it enables laser resonance ionization spectroscopy to develop laser excitation schemes suitable for the solid-state laser systems used with TRIUMF's resonant ionization laser ion source . Also, it allows for possible improvement of current ion sources and validation of new designs. The test stand employs a copy of the ion optics used on-line, so that results can be transferred directly to radioactive ion beam production. Due to space restrictions and the need for rapid mass scans, a quadrupole mass spectrometer is used as a mass separator. One of the first experiments conducted on the laser ion source test stand (LIS STAND) was resonant ionization spectroscopy of gallium to improve on the ionization scheme previously used on-line, so that low yield isotopes (e.g., (62)Ga) become available for experiments. Different Rydberg series in gallium were observed and autoionizing states were searched for. The overall LIS STAND system performance, characteristics, and the first resonant ionization spectroscopy are described.

CRIS: A new method in isomeric beam production

The Collinear Resonance Ionization Spectroscopy (CRIS) experiment at ISOLDE, CERN, uses laser radiation to stepwise excite and ionize an atomic beam for the purpose of ultra-sensitive detection of rare isotopes, and hyperfine-structure measurements. The technique also offers the ability to purify an ion beam that is heavily contaminated with radioactive isobars, including the ground state of an isotope from its isomer, allowing decay spectroscopy on nuclear isomeric states to be performed. The isomeric ion beam is selected by resonantly exciting one of its hyperfine structure levels, and subsequently ionizing it. This selectively ionized beam is deflected to a decay spectroscopy station (DSS). This consists of a rotating wheel implantation system for alpha- and beta-decay spectroscopy, and up to three germanium detectors around the implantation site for gamma-ray detection. Resonance ionization spectroscopy and the new technique of laser assisted nuclear decay spectroscopy have recently been performed at the CRIS beam line on the neutron-deficient francium isotopes. Here an overview of the two techniques will be presented, alongside a description of the CRIS beam line and DSS. © Owned by the authors, published by EDP Sciences, 2013.

Acetylation makes the difference: a joint experimental and theoretical study on low-lying electronically excited states of 9H-adenine and 9-acetyladenine

Vibronic spectra of 9H-adenine, 9-acetyladenine and several alkyladenines have been recorded by resonant two-photon ionization spectroscopy of the laser-desorbed molecules, entrained in a molecular beam. While adenine and the alkyladenines exhibit similar electronic spectra, 9-acetyladenine behaves considerably different. Theoretical absorption spectra of 9H-adenine and 9-acetyladenine were calculated using the combined density functional theory/multi-reference configuration interaction approach and using second order coupled cluster theory, in order to explain striking differences in the experimental spectra. The major differences between the 9H-adenine and the 9-acetyladenine absorption spectra can be traced back to the different configurations, which contribute to the excitations, both of the lowest ππ* and the nπ* states. While the excitations in 9H-adenine are localized in the chromophore, they show considerable charge transfer character from the chromophore to the acetyl group in the case of 9-acetyladenine.

A dedicated decay-spectroscopy station for the collinear resonance ionization experiment at ISOLDE

A new decay-spectroscopy station (DSS) has been developed to be coupled to the collinear resonance ionization spectroscopy (CRIS) beam line at CERN-ISOLDE. The system uses a rotatable wheel with ten 20μg/cm2 carbon foils as beam implantation sites for the efficient measurement of charged decay products. Silicon detectors are placed on either side of the carbon foil in an optimal geometry to cover a large solid angle for detecting these charged particles. In addition to the silicon detectors at the on-beam axis position, a second pair of off-beam axis detectors are placed at the wheel position 108° away, allowing longer-lived species to be studied. Up to three high purity germanium detectors can be placed around the chamber for particle-gamma correlated measurement. The radioactive beam is transported through the CRIS beam line before implantation into a carbon foil at the DSS. All materials used in the DSS are UHV-compatible to maintain high vacuum conditions required by the CRIS beam line. This paper describes the DSS and presents the first data collected at the setup during the commissioning run with 221Fr.

The in-gas-jet laser ion source: Resonance ionization spectroscopy of radioactive atoms in supersonic gas jets

New approaches to perform efficient and selective step-wise resonance ionization spectroscopy (RIS) of radioactive atoms in different types of supersonic gas jets are proposed. This novel application results in a major expansion of the in-gas laser ionization and spectroscopy (IGLIS) method developed at KU Leuven. Implementation of resonance ionization in the supersonic gas jet allows to increase the spectral resolution by one order of magnitude in comparison with the currently performed in-gas-cell ionization spectroscopy. Properties of supersonic beams, obtained from the de Laval-, the spike-, and the free jet nozzles that are important for the reduction of the spectral line broadening mechanisms in cold and low density environments are discussed. Requirements for the laser radiation and for the vacuum pumping system are also examined. Finally, first results of high-resolution spectroscopy in the supersonic free jet are presented for the 327.4nm 3d104s 2S1/2→ 3d104p 2P1/2 transition in the stable 63Cu isotope using an amplified single mode laser radiation.

New laser setup at the IRIS facility. Magnetic moments and mean squared charge radii of neutron deficient Tl isotopes

A new laser installation for the resonance ionization spectroscopy in a laser ion source and for rare isotope production has been put into operation at the IRIS mass-separator, working on-line with the 1 GeV proton beam of the Petersburg Nuclear Physics Institute synchrocyclotron. Isotope shift and hyperfine splitting of 276.9 nm atomic transition in the long chain of Tl isotopes and isomers have been measured. New data on the magnetic moments and changes in mean squared charge radius for 183,184,185,185m,186m2,195m,197mTl have been obtained.

Rotamers and isotopomers of 3-chloro-5-fluoroanisole studied by resonant two-photon ionization spectroscopy and theoretical calculations

The ab initio and density functional theory (DFT) calculations reveal that two rotamers, denoted by cis and trans 3-chloro-5-fluoroanisole (3C5FA), are stable for each of the S0, S1, and D0 states. In the one-color resonant two-photon ionization (R2PI) spectra, the band origins of the S1←S0 electronic transition (00 bands) of cis35Cl-3C5FA and cis37Cl-3C5FA are both located at 36,468±3cm−1, while the 00 bands of trans35Cl-3C5FA and trans37Cl-3C5FA are found to be 36,351±3 and 36,354±3cm−1. The two rotamers display very similar vibrational frequencies in the S1 state, and the observed active modes mainly involve the in-plane ring deformation vibrations. By the two-color R2PI spectroscopy, the adiabatic ionization energies (IEs) of both isotopomers of 3C5FA are determined to be 69,720±15cm−1 for the cis rotamer and 69,636±15cm−1 for the trans rotamer. The substitution, conformation, and isotope effects on the properties of 3C5FA, including the molecular structures, vibrational frequencies, and electronic transition and ionization energies, were also discussed in detail.