48 research outputs found
Optical cycling in charged complexes with Ra-N bonds
The extension of laser cooling and trapping techniques to polyatomic
molecular ions would have advanced scientific applications such as search of
physics outside of the Standard Model, ultracold chemistry etc. We apply the
Fock space relativistic coupled cluster method to study low-lying electronic
states of molecular ions with Ra--N bonds, namely RaNCH, RaNH and
RaNCCH. Prospects of laser cooling of these species are estimated, and
the peculiarities of unpaired-electron distributions are analyzed from the
point of view of the molecular electronic structure. RaNH and
RaNCCH are the first symmetric top molecular ions expected to be suitable
for direct laser cooling
Compound-tunable embedding potential method to model local electronic excitations on -element ions in solids: Pilot relativistic coupled cluster study of Ce and Th impurities in yttrium orthophosphate, YPO
A method to simulate local properties and processes in crystals with
impurities via constructing cluster models within the frame of the
compound-tunable embedding potential (CTEP) and highly-accurate {\it ab initio}
relativistic molecular-type electronic structure calculations is developed and
applied to the Ce and Th-doped yttrium orthophosphate crystals, YPO, having
xenotime structure. Two embedded cluster models are considered, the "minimal"
one, YO@CTEP, consisting of the central Y cation and its
first coordination sphere of eight O anions (i.~e.\ with broken P--O
bonds), and its extended counterpart, Y(PO)@CTEP, implying
the full treatment of all atoms of the PO anions nearest to the
central Y cation. CTEP denote here the corresponding
cluster environment described within the CTEP method. The relativistic
Fock-space coupled cluster (FS RCC) theory is applied to the minimal cluster
model to study electronic excitations localized on Ce and Th
impurity ions. Calculated transition energies for the cerium-doped xenotime are
in a good agreement with the available experimental data (mean absolute
deviation of ca.0.3 eV for type transitions). For the thorium-doped
crystal the picture of electronic states is predicted to be quite complicated,
the ground state is expected to be of the character. The uncertainty for
the excitation energies of thorium-doped xenotime is estimated to be within
0.35 eV. Radiative lifetimes of excited states are calculated at the FS RCC
level for both doped crystals. The calculated lifetime of the lowest state
of Ce differs from the experimentally measured one by no more than
twice
Relativistic Calculations on the Electric Dipole Transition Probabilities of the RbAr Exciplex
Accurate evaluation of electric dipole (E1) transition probabilities in exciplexes formed by an alkali atom (M) and rare gas (Rg) atom(s) is essential for modelling optically pumped M–Rg laser media. We present a simple finite-difference scheme of ab initio calculations of E1 transition moments in the RbAr exciplex in the frames of relativistic Fock space coupled cluster approach
Relativistic Calculations on the Electric Dipole Transition Probabilities of the RbAr Exciplex
Accurate evaluation of electric dipole (E1) transition probabilities in exciplexes formed by an alkali atom (M) and rare gas (Rg) atom(s) is essential for modelling optically pumped M–Rg laser media. We present a simple finite-difference scheme of ab initio calculations of E1 transition moments in the RbAr exciplex in the frames of relativistic Fock space coupled cluster approach
Radiative lifetimes of the NaRb C(3)
Radiative lifetimes for 2≤v′≤44 rovibronic C1Σ+ state levels of NaRb and quenching collision cross-sections with Rb atoms have been directly measured in a thermal cell by detecting time resolved laser induced fluorescence after pulsed excitation. Many body multipartitioning theory was applied to calculate C1Σ+-X1Σ+ and C1Σ+-A1Σ+ transition dipole moments. The relevant
ab initio matrix elements were converted to the C1Σ+ state radiative lifetimes. The strong spin-orbit A1Σ+∼ b3Π coupling effect on the total C → A transition probabilities and lifetimes of the C1Σ+ state is discussed. The measured radiative lifetimes show a decrease from 61 to 34 ns as the v′ values increase, the results being in good agreement with calculations. The averaged collisional quenching cross-section value σ=(3±1)×10-14 cm2 was determined for NaRb (C1Σ+) + Rb collisions from the Stern-Volmer plots