Two-color Resonant Ionization Research Articles

Development of two-color resonant ionization sputtered neutral mass spectrometry and microarea imaging for Sr

Two-color resonant laser ionization sputtered neutral mass spectrometry offers high elemental selectivity. In this study, two-color resonance ionization in sputtered neutral Sr was confirmed by combining a grating type Ti:sapphire laser system and a time-of-flight secondary ion mass spectrometry (TOF-SIMS) system. The authors compared the ionization efficiencies of Sr of the two-color three-photon ionization scheme 1 (first step: 460.862 nm; second step: 767.519 nm) and the two-color two-photon ionization scheme 2 (first step: 460.862 nm; second step: 405.200 nm). The resonant ionization efficiency of the latter was found to be 50 times larger than that of the former. Finally, the authors mapped the microarea distribution of Sr by two-color resonant ionization sputtered neutral mass spectrometry.

Study of Eu 4f76snl Rydberg states

The three-step two-color resonant ionization method and three-step three-color isolated-core excitation (ICE) technique are used to study the spectra of the highly excited bound states systematically, either Eu 4f76snl Rydberg states or other valence states converging to the higher ionization limits. Specifically, the highly excited bound states are populated from the ground state via three different 4f76s6p intermediate states, thereby establishing the three different excitation schemes. The schemes are designed to allow us to assign a J-quantum number uniquely to a given highly excited state with the selection rules of J-quantum number for each excitation scheme by comparing their corresponding photoionization spectra, which are obtained with three-step two-color resonant ionization method. By tuning the wavelength of the second laser, the 56 highly excited bound states located in the energy region between 42250 cm-1 and 44510 cm-1 are detected. To explore their spectroscopic information, more efforts have been made 1) to judge whether an excited state is a bound Rydberg state and to observe whether it may be excited further to an autoionizing state by using the ICE technique; 2) to deduce the principal quantum number of the given bound Rydberg states, and to observe whether they are converged to the same ionization limit by calculating their quantum defects with respect to several ionization limits. Based on the above manipulations, all detected highly excited bound states can be classified as the two categories: bound Eu 4f76snl Rydberg states and other valence states converging to the higher ionization limits, such as the Eu 4f75dnl states. Specifically, to fulfill the ICE technique, it is necessary to make a resonance transition from the 4f76snl Rydberg states to the 4f76p1/2nl autoionizing states with the third dye laser whose wavelength is scanned around the Eu 4f76s+-4f76p1/2+ ionic line. Once the Eu 4f76snl Rydberg states are recognized with the ICE technique, the identification of their orbital quantum numbers is a primary task to determine their electron configurations. With all the efforts mentioned and existing information, three Rydberg states can be assigned to the 4f76s10s(8S9/2), 4f76s9d(8D9/2) and 4f76s9d(6D7/2), whereas the rest can be regarded as highly excited valence states.

Polarization-based isotope-selective two-color photoionization of atomic samarium using broadband lasers

An isotope separation method based on polarization selection rules is applied to atomic samarium by using two-color resonance ionization spectroscopy with broadband lasers. In this method, odd isotopes with nonzero nuclear spin are selectively excited, while even isotopes with zero nuclear spin are prohibited from excitation using two parallel linearly polarized lasers. We have identified a two-color excitation scheme 0 cm−1 (J = 0) → 15650.5 cm−1 (J = 1) → 33116.8 cm−1 (J = 1) → Sm+ for selective excitation of the odd isotopes of Sm I. Using this scheme, selective excitation of odd isotopes of Sm I (147Sm and 149Sm) with an isotopic selectivity better than 40 has been demonstrated. In addition, the effect of different polarization states of the excitation lasers and relative polarization angle between them on the selectivity of odd isotopes has also been studied. The dependence of the even mass isotope signal on the relative polarization angle followed sin2θ, which is in excellent agreement with theoretical predictions.

New even-parity high-lying levels of Sm I and measurement of isotope shifts by two-color resonance ionization mass spectrometry

In this work, we investigate the even-parity high-lying levels of Sm I in the energy region 33136–33960cm−1 by performing two-color three-photon resonance ionization spectroscopy in an atomic beam coupled to a time-of-flight mass spectrometer using two tunable pulsed dye lasers. We observe twenty-one new and confirm eight previously reported even-parity energy levels of Sm I in this spectral region. Absolute energies of these levels are determined with an accuracy of ±0.3cm−1. Using electric dipole selection rule, total angular momentum (J-value) of the most newly observed levels is assigned uniquely. Further, employing two-color three-step resonance ionization mass spectrometry, we measure the isotope shift between 154Sm and 144Sm of sixteen high-lying levels with a moderate accuracy of ±30mK.

Isotopically Resolved Photoelectron Imaging Unravels Complex Atomic Autoionization Dynamics by Two-Color Resonant Ionization

Angle-resolved electron spectroscopy in coincidence with high-resolution mass spectroscopy has been applied to study two-color resonant photoionization in atomic xenon. Separation of different isotopes enabled us to extract results for the electronic dynamics free from depolarization effects, which are generally introduced by the coupling of the electronic and nuclear angular momenta. The concerted experimental and theoretical analysis of the photoelectron angular distributions in the region of an autoionizing resonance emphasizes the strong sensitivity of the observed structures to the fine details of the treatment of the underlying dynamics.

Two-color resonance ionization spectroscopy of highly excited titanium atoms

We performed two-color resonance ionization spectroscopy for studying highly excited states of titanium. We obtained high-resolution spectra of the Rydberg and autoionization series using three intermediate states. To observe the appropriate series, we considered mixed configurations of the intermediate states. The convergence limits of the observed series depended on the intermediate states. Using the Rydberg formula and convergence limit estimation, we could provide a tentative assignment to almost all the fine structure levels in the obtained spectra. From the analyses of the two regions, we derived the ionization potential of titanium as 55 072.5±0.1cm−1.

Two-color resonance ionization spectroscopy of Rydberg states of hafnium atoms

We performed two-color resonance ionization spectroscopy to study the highly excited states of hafnium. We obtained the high-resolution spectra of the Rydberg series converging to the first ionization limit. These series of states have not been previously observed. From analyses of the main Rydberg series with Rydberg formula, we derived the ionization potential of hafnium as $55047.9\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. Comparing the spectra obtained through three different intermediate states, we could assign the $J$ value of all the series in a certain energy region.

Rotationally Resolved (1 + 1‘) Resonance-Enhanced Multiphoton Ionization (REMPI) of CaR (R = H, D) in Supersonic Beams: CaR X 2Σ+ (υ‘ ‘ = 0) → CaR* B 2Σ+ (υ‘= 0, 1) → CaR+ X Σ+

We report on a laser-spectroscopic study of the CaH and CaD radicals in a supersonic beam, generated in a reaction of laser-sputtered Ca atoms and a pulsed beam of H2 or D2, seeded in helium. The rotational levels of the electronic ground-state X 2Σ+ (υ‘ ‘ = 0, N‘ ‘ ≤ 10) were probed by two-color resonance ionization mass spectrometry(1 + 1‘) resonance-enhanced multiphonon ionization (REMPI)via the intermediate B 2Σ+ (υ‘ = 0, 1) rovibronic levels. Rotational constants for the B-state were derived, including the spin splitting parameters γυ‘, which have been determined in the case of CaD for the first time: γ0 = −0.409(7) cm-1 and γ1 = −0.398(8) cm-1 for CaD (B 2Σ+), and γ0 = −0.792(15) cm-1 and γ1 = −0.765(16) cm-1 for CaH (B 2Σ+). The comparison between the rotational level energies of the F1 and F2 spin substates of the two isotopomers revealed the onset of perturbation in CaH B 2Σ+ (υ‘ = 0), at N‘ ≅ 0, by the presence of the vibronic state A 2Π (υ‘ = 1). Although this perturbation is documented for υ‘...

Structural and Vibrational Assignment of p-Methoxyphenethylamine Conformers

A combined wide range of laser spectroscopic techniques and computational quantum chemistry are used to investigate conformer landscapes of large substituted aromatic molecules. The spectroscopic techniques include laser-induced fluorescence (LIF), high-resolution LIF, resonance-enhanced multiphoton ionization (REMPI) with mass detection, two-color resonance ionization with mass detection (R2PI), laser dispersed emission (DE), and ion-dip hole burning (HB). These techniques are balanced with extensive ab initio DFT calculations at the B3LYP/6-31+G* and B3LYP/6-311+G* levels. These methods have been applied to investigate the nine possible conformations of the p−methoxyphenethylamine (MPEA) neurotransmitter molecule. Even when all the spectroscopic techniques play important roles, two color ionization energy (IE) threshold determinations have proven to be especially useful in the study. The gauche and anti conformers exhibit different ionization energy values, and even the amino hydrogen orientation influences their energies. The results allow the unequivocal identification of seven conformer structures which are further confirmed by the assignment of their vibrational spectra. A discussion on the intramolecular interactions, including the N−H···π hydrogen bonding correlation with the molecular stability in the light of the theoretical and experimental results, is also presented.

Abundance ratios of mercury isotopes by 6 s 6 p 3 P 1 -intermediate state excitation with resonance ionization mass spectrometry

The isotope-selective excitation of mercury via the 6s6p3P1 intermediate state excitation is studied with two-color resonance ionization mass spectrometry to determine abundance ratios of stable mercury isotopes. Lifetime, isotopic shifts, and hyperfine structure (HFS) splittings are measured. Atomic hyperfine interaction constants are determined. Line strengths of the ten components of the 6s21S0→ 6s6p3P1 transition are used for isotope ratio determinations. Ion signal intensities of even-mass components directly give the isotopic abundance, in contrast to the odd-mass components, for which the sum of the HFS components results in an anomalously high response for the isotopic abundance. The laser bandwidth dependence of the excitation and population probabilities of magnetic HFS sublevels due to linear polarization of the radiation are discussed. These considerations yield reasonable values for the apparent odd-mass isotope abundance.

Observation of Ultracold Ground-State Potassium Molecules

Ultracold potassium molecules are produced in the $X^{1}\ensuremath{\Sigma}_{g}^{+}$ electronic ground state by photoassociation in a magneto-optical trap. They are detected sensitively and selectively by use of two-color resonant ionization, followed by time-of-flight mass spectroscopy. We observe deeply bound molecules with $\ensuremath{\nu}\ensuremath{\cong}36$, at a temperature of about $300\ensuremath{\mu}\mathrm{K}$. Presently about 1000 molecules/sec are produced, and much higher production rates should be attainable in the future.

Resonance ionization spectroscopy and analysis on even-parity states of Pb

Two-color resonance ionization spectroscopies of Pb, even parity, J=0, 1, and 2 levels were performed and their term values were analyzed with multichannel quantum defect theory. We have observed 6pnp(1/2,1/2${)}_{0}$ (28\ensuremath{\le}n\ensuremath{\le}50), 6p7p(3/2,3/2${)}_{0}$, 6pnp(1/2,3/2${)}_{1}$ (14\ensuremath{\le}n\ensuremath{\le}27), 6pnp(1/2,3/2${)}_{2}$ (42\ensuremath{\le}n\ensuremath{\le}54), and 6pnf 1/2[5/2${]}_{2}$ (28\ensuremath{\le}n\ensuremath{\le}51). Fitting multichannel quantum defect theory (MQDT) parameters to minimize deviation between the observed and theoretical energy values, we determined quantum defects ${\mathrm{\ensuremath{\mu}}}_{\mathrm{\ensuremath{\alpha}}}$ and unitary matrix elements ${\mathit{U}}_{\mathit{i}\mathrm{\ensuremath{\alpha}}}$ for J=0, 1, and 2 even-parity levels. Calculating theoretical energy values and determining their assignment with MQDT, we assigned observed levels and predicted unobserved levels and perturbers. Admixture coefficients for perturbing levels of J=0, 1, and 2 were calculated in order to ensure their assignments. \textcopyright{} 1996 The American Physical Society.

Pulsed single-mode laser ionization of hyperfine levels of zirconium-91

We identify a considerable improvement in proposed schemes for isotopic depletion of zirconium-91 on the basis of the atomic vapor laser isotope separation (AVLIS) method. The improvement lies in applying a single-longitudinal-mode dye laser for selective excitation of all hyperfine split levels of the ground state of zirconium-91. High-resolution laser-induced fluorescence spectroscopy of atomic beams of zirconium produced through laser vaporization–supersonic expansion has been used to identify transitions of zirconium with suitable hyperfine structure. Casimir magnetic-dipole and electric-quadrupole coupling constants and isotope shifts have been derived and are reported for five excited configurations. Suitable intermediate levels in a multistep resonance ionization pathway have been identified by two-color resonance ionization spectroscopy. Isotope depletion has been demonstrated on one ground-state-transition ( z F33∘←a F32at 593.7 nm) by using a specially constructed pulsed, single-longitudinal-mode dye-laser oscillator. Prospects and future directions in zirconium AVLIS are discussed.

Resonance ionization mass spectrometry of technetium

Three-photon, two-color resonance ionization mass spectrometry (RIMS) is described for technetium. The wavelengths used to effect ionization of Tc are between 420 and 620 nm. Twenty-two unique ionization paths originating in the atomic ground state are observed and identified. An unknown fraction of the sample Tc is vaporized in molecular form and cannot be addressed by normal atomic photoionization methods.