Jiande Han’s research while affiliated with Emory University and other places

Electronic spectra for OThF have been recorded using fluorescence excitation and two-photon resonantly enhanced ionization techniques. Multiple vibronic bands were observed in the 340–460 nm range. Dispersed fluorescence spectra provided ground state vibrational constants and evidence of extensive vibronic state mixing at higher excitation energies. Two-photon ionization measurements established the ionization energy for OThF of 6.283(5) eV. To guide the assignment of the OThF spectra, electronic structure calculations were carried out using relativistic equation-of-motion coupled-cluster singles and doubles methods. These calculations indicated that spin–orbit induced mixing of the 3²A″ and 4²A′ states was mediated by a seam of potential energy surface intersections.

The optically pumped rare-gas metastable laser is capable of high-intensity lasing on a broad range of near-infrared transitions for excited-state rare gas atoms (Ar*, Kr*, Ne*, Xe*) diluted in flowing He. The lasing action is generated by photoexcitation of the metastable atom to an upper state, followed by collisional energy transfer with He to a neighboring state and lasing back to the metastable state. The metastables are generated in a high-efficiency electric discharge at pressures of ∼0.4 to 1 atm. The diode-pumped rare-gas laser (DPRGL) is a chemically inert analogue to diode-pumped alkali laser (DPAL) systems, with similar optical and power scaling characteristics for high-energy laser applications. We used a continuous-wave linear microplasma array in Ar/He mixtures to produce Ar(1s5) (Paschen notation) metastables at number densities exceeding 1013 cm-3. The gain medium was optically pumped by both a narrow-line 1 W titanium-sapphire laser and a 30 W diode laser. Tunable diode laser absorption and gain spectroscopy determined Ar(1s5) number densities and small-signal gains up to ∼2.5 cm-1. Continuous-wave lasing was observed using the diode pump laser. The results were analyzed with a steady-state kinetics model relating the gain and the Ar(1s5) number density.

The polyatomic molecules YbOH and YbOCH3 have been recognized as being of potential value for spectroscopic experiments that explore charge-parity and time-reversal symmetry violation effects. These measurements require very high precision, which, in turn, will necessitate that the molecules be manipulated at ultracold temperatures. Both YbOH and YbOCH3 have electronic transitions that appear suitable for laser cooling (Ã2Π1/2−X̃2Σ+ and Ã2E1/2−X̃2A1, respectively) but the currently available spectroscopic data are not sufficient to determine the extent to which population leaks may compromise the optical cooling processes. A further complication is that the quantum states of interest for these measurements will need to be selectively populated. The ÖX̃ band systems of both YbOH and YbOCH3 show evidence of vibronic perturbations, such that there are unassigned vibronic features at energies that are just above the origin bands. In the present study we have recorded spectra for the à 2Π1/2−X̃2Σ+ transition of jet-cooled YbOD to facilitate the vibronic assignments. In addition, spectra for the B̃2Σ+−X̃2Σ+ transition of YbOH were recorded, establishing the origin band at 20 473.8 cm−1. Previously, the reaction of Yb with CH3OH has been used to generate gas-phase YbOCH3. As this reaction also yields YbOH, there have been complications in spectroscopic studies of YbOCH3 due to overlap of the ÖX̃ band systems. To identify specific regions of overlap, resonantly enhanced two-photon ionization spectra were recorded using mass-resolved detection of the YbOH+ and YbOCH3+ ions. These data confirmed the overlap of vibronic bands near 17 640 and 17 680 cm−1. Two-photon ionization spectroscopy also provided accurate ionization energies (IE), IE(YbOH)=45788(10) and IE(YbOCH3)=45283(10)cm−1. The IE for YbOH is relevant to problems encountered in previous attempts to determine the bond-dissociation energy of YbOH+.

YbF has been identified as a molecule that can be used to investigate charge-parity symmetry violations that are beyond the standard model of particle physics. Cooling to sub-milli-Kelvin is advantageous for experiments that probe manifestations of these symmetry violations. One approach involves laser cooling of YbF via the A2Π1/2−X2Σ+ transition. However, it appears that cooling by means of this transition may be limited by the radiative loss of population from the cooling cycle. YbF has low-energy states that arise from the Yb+(4f136s2)F− configuration. Recent theoretical calculations [C. Zhang et al., J. Mol. Spectrosc. 386, 111625 (2022)] predict that radiative decay from A2Π1/2 to the 4f136s2 states occurs with a branching fraction of approximately 10−3. In the present study we have used dispersed laser induced fluorescence spectroscopy to observe the lowest energy 4f136s2 states. These measurements were carried out using excitation of previously unobserved YbF transitions in the near UV spectral range. An accurate ionization energy (IE) of 48703±5cm−1 for YbF is also reported. A two-color photoionization technique was used to determine the IE and observe the v+=0−3 vibrational levels of YbF+X1Σ+.

Diatomic UO has more than 48 bound states within 10000 cm-1 of the ground state. This electronic state congestion has been attributed to interleaved states from the electronic configurations U2+(5f37s)O2- and U2+(5f27s2)O2-, respectively. Ligand field theory predicts that each electronic configuration will exhibit states with distinguishable, characteristic vibrational and rotational constants. However, vibronic state mixing modifies the observed vibration-rotation constants, leading to uncertainty in the configurational assignments. The permanent electric dipole moment (μe) of an electronic state should also manifest a value that is characteristic of the parent electronic configuration. μe and other electrostatic and magnetostatic properties should be less influenced by the vibronic state mixing, providing more robust indicators for configurational assignments. In the present study, we have measured the μe values for four electronic states of UO. The results clearly demonstrate that the ground state (X(1)4) and the first electronically excited state ((2)4) are derived from the U2+(5f37s)O2- and U2+(5f27s2)O2- configurations, respectively.

YbF has been identified as a molecule that can be used to investigate charge-parity symmetry violations that are beyond the Standard Model of particle physics. Cooling to sub-milli-Kelvin is advantageous for experiments that probe manifestations of these symmetry violations. One approach involves laser cooling of YbF via the A2P1/2-X2S+ transition. However, it appears that cooling by means of this transition may be limited by the radiative loss of population from the cooling cycle. YbF has low-energy states that arise from the Yb+(4f136s2)F- configuration. Recent theoretical calculations predict (Zhang et al J. Mol. Spectrsc. 386 11625 (2022)) that radiative decay from A2{\Pi}1/2 to the 4f136s2 states occurs with a branching fraction of approximately 10-3. In the present study we have used dispersed laser induced fluorescence spectroscopy to the observe the lowest energy 4f136s2 states. These measurements were carried out using excitation of previously unobserved YbF transitions in the near UV spectral range. An accurate ionization energy (IE) for YbF is also reported. A two-color photoionization technique was used to determine the IE and observe the v+=0-3 vibrational levels of YbF+ X1S+.