Physical Chemistry Chemical Physics

Electronic states and spin-forbidden cooling transitions of AlH and AlF

Nathan Wells, Ian C. Lane

Published Jan 1, 2011• 99 citations

Abstract

The feasibility of laser cooling AlH and AlF is investigated using ab initio quantum chemistry. All the electronic states corresponding to the ground and lowest two excited states of the Al atom are calculated using multi-reference configuration interaction (MRCI) and the large AV6Z basis set for AlH. The smaller AVQZ basis set is used to calculate the valence electronic states of AlF. Theoretical Franck-Condon factors are determined for the A(1)Π→ X(1)Σ(+) transitions in both radicals and found to agree with the highly diagonal factors found experimentally, suggesting computational chemistry is an effective method for screening suitable laser cooling candidates. AlH does not appear to have a transition quite as diagonal as that in SrF (which has been laser cooled) but the A(1)Π→ X(1)Σ(+) transition transition of AlF is a strong candidate for cooling with just a single laser, though the cooling frequency is deep in the UV. Furthermore, the a(3)Π→ X(1)Σ(+) transitions are also strongly diagonal and in AlF is a practical method for obtaining very low final temperatures around 3 μK.

DOI: 10.1039/c1cp21313j

Related papers

Ab initio studies on the spin-forbidden cooling transitions of the LiRb molecule

Yang You, Chuan‐Lu Yang, Qingqing Zhang +3 more

The spin-forbidden cooling of the LiRb molecule is investigated based on ab initio quantum chemistry calculations. The multireference configuration interaction method is used to generate the potential energy curves (PECs) of the ground state X(1)Σ(+) and the low-lying excited states a(3)Σ(+), B(1)Π, and b(3)Π. The spin-orbit coupling effects for the PECs and the transition dipole moments (TDMs) between the X(1)Σ(+), b(3)Π and a(3)Σ(+) states are also calculated. The analytical functions for the PECs are deduced. The rovibrational energy levels, the spectroscopic parameters and the Franck-Condon factors (FCF) are determined by solving the Schrödinger equation of nuclear movement with the obtained analytical functions. The b(3)Π0 ↔ X(1)Σ(+) and b(3)Π1 ↔ X(1)Σ(+) transitions have highly diagonal distributed FCFs and non-zero TDMs, demonstrating that the LiRb molecule could be a very promising candidate for laser cooling. Therefore, a three-cycle laser cooling scheme for the molecule has been proposed based on these two spin-forbidden transitions. Using the radiative lifetime and linewidth calculated from the obtained TDM functions, we present further analysis of the cooling of LiRb and the corresponding KRb molecule. The transition b(3)Π0 ↔ X(1)Σ(+) is found to be a practical transition to cool the LiRb molecule, and a sub-microkelvin cool temperature could be reached for the KRb molecule using a similar laser cooling scheme.

Physical Chemistry Chemical PhysicsJan 1, 201625 citations

Feasibility study of laser cooling of InF molecule

Quan-Shun Yang, Tao Gao

By employing ab initio quantum chemistry method, we investigate the feasibility of laser cooling InF molecule. Four low-lying electronic states (X1Σ+, C1Π, 3Π and 23Π) of InF have been calculated using the multi-reference configuration interaction (MRCI) method. The spin-orbit coupling effects are also taken into account in the electronic structure computation at the MRCI level. The highly diagonal Franck-Condon factors for C1Π → X1Σ+ transitions are estimated. The radiative lifetime of the C1Π (v′ = 0) state is about 2.22 ns, which is found to be enough short for rapid laser cooling. Though the cooling wavelength of InF is located in the short-wavelength ultraviolet light (UVC), a frequency quadrupled Ti: sapphire laser (189–235 nm) could be capable of generating laser transition wavelength of InF. Furthermore, the C1Π → X1Σ+ transitions perhaps can be followed by the B3Π1 → X1Σ+0+ transitions to attain a lower Doppler temperature. Meanwhile, for achieving quasi-closed transition cycle of InF molecule, we investigate the hyperfine structure of the lowest state X1Σ+. Overall, the present results indicate the possibility of laser cooling InF molecules.

Molecular PhysicsJan 20, 20177 citations

Laser cooling of MgCl and MgBr in theoretical approach

Mingjie Wan, Juxiang Shao, Yufeng Gao +5 more

Ab initio calculations for three low-lying electronic states (X(2)Σ(+), A(2)Π, and 2(2)Π) of MgCl and MgBr molecules, including spin-orbit coupling, are performed using multi-reference configuration interaction plus Davidson correction method. The calculations involve all-electronic basis sets and Douglas-Kroll scalar relativistic correction. Spectroscopic parameters well agree with available theoretical and experimental data. Highly diagonally distributed Franck-Condon factors f00 for A(2)Π3/2,1/2 (υ' = 0) → X(2)Σ(+) 1/2 (υ″ = 0) are determined for both MgCl and MgBr molecules. Suitable radiative lifetimes τ of A(2)Π3/2,1/2 (υ' = 0) states for rapid laser cooling are also obtained. The proposed laser drives A(2)Π3/2 (υ' = 0) → X(2)Σ(+) 1/2 (υ″ = 0) transition by using three wavelengths (main pump laser λ00; two repumping lasers λ10 and λ21). These results indicate the probability of laser cooling MgCl and MgBr molecules.

The Journal of Chemical PhysicsJul 8, 201528 citations

Theoretical investigation for the laser cooling of LuH+ molecular cation

Fan Qin, Qing Zhang, Mingjie Wan +1 more

The potential energy curves and transition dipole moments of seven Λ-S states and six Ω states of LuH+ cation are calculated by using the multireference configuration interaction method plus Davidson correction with the pseudopotential electron basis set, and the spectroscopic parameters of the bound states are obtained. The spin–orbit coupling effect is considered in the calculations. The Franck–Condon factors (FCFs) and the Einstein spontaneous emission coefficients are obtained. The results indicate that the A2Δ3/2(ν′ = 0) ↔ X2Σ+1/2(ν″ = 0) and B2Π1/2(ν′ = 0) ↔ X2Σ+1/2 (ν″ = 0) transitions provide highly diagonally distributed FCFs. Spontaneous radiative lifetimes of A2Δ3/2 (ν′ = 0) and B2Π1/2 (ν′ = 0) excited states are both obtained. The cooling schemes of LuH+ cation are obtained using the ab initio method. For the B2Π1/2 ↔ X2Σ+1/2 transition, the influence of the intermediate state on the construction of quasi-closed cyclic transitions can be neglected. A main pump laser and two repumping lasers are required to construct the A2Δ3/2 ↔ X2Σ+1/2 and B2Π1/2 ↔ X2Σ+1/2 quasi-cycling transitions for laser cooling of LuH+ molecular cation. The results in this work provide reliable theoretical guidance for further experiments of laser cooling of LuH+ cation.

AIP AdvancesOct 1, 20242 citations

Spectroscopic characterization of the a3Π state of aluminum monofluoride

Nicole Walter, Maximilian Doppelbauer, Silvio Marx +6 more

Spectroscopic studies of aluminum monofluoride (AlF) have revealed its highly favorable properties for direct laser cooling. All Q lines of the strong A1Π ← X1Σ+ transition around 227 nm are rotationally closed and thereby suitable for the main cooling cycle. The same holds for the narrow, spin-forbidden a3Π ← X1Σ+ transition around 367 nm, which has a recoil limit in the µK range. We here report on the spectroscopic characterization of the lowest rotational levels in the a3Π state of AlF for v = 0–8 using a jet-cooled, pulsed molecular beam. An accidental AC Stark shift is observed on the a3Π0, v = 4 ← X1Σ+, v = 4 band. By using time-delayed ionization for state-selective detection of the molecules in the metastable a3Π state at different points along the molecular beam, the radiative lifetime of the a3Π1, v = 0, J = 1 level is experimentally determined as τ = 1.89 ± 0.15 ms. A laser/radio frequency multiple resonance ionization scheme is employed to determine the hyperfine splittings in the a3Π1, v = 5 level. The experimentally derived hyperfine parameters are compared to the outcome of quantum chemistry calculations. A spectral line with a width of 1.27 kHz is recorded between hyperfine levels in the a3Π, v = 0 state. These measurements benchmark the electronic potential of the a3Π state and yield accurate values for the photon scattering rate and for the elements of the Franck–Condon matrix of the a3Π–X1Σ+ system.

arXiv:2112.09498The Journal of Chemical PhysicsFeb 22, 20227 citations

Theoretical Investigation on the Laser Cooling of AlD Molecule

LI Shengzhou, Zhou Ying, Xing Wei

The potential energy curves for four Λ-S and eight Ω states of the AlD molecule are calculated by using the valence internally contracted multireference configuration interaction approach with the Davidson modification (icMRCI+Q). The core-valence correlation and relativistic corrections are included. The extrapolation of potential energies to the complete basis set limit is made. Transition dipole moments (TDMs) between the six bound Ω states are also calculated by the icMRCI approach. The calculated spectroscopic constants are in good agreement with the available experimental data and theoretical values. Based on the obtained potential energy curves and transition dipole moments, highly diagonal Franck-Condon factors and vibrational branching ratios are determined for the A1π1(υ'=0,1)→X1Σ+0+(υ'') transition, short spontaneous radiative lifetime and narrow radiative width for the excited state A1π1 (υ'=0, 1) are also predicted. On this account, the optical scheme of the laser cooling for AlD molecule is constructed with A1π1(υ')↔X1Σ+0+(υ'') as the close-loop transition. The proposed laser drives X1Σ+0+(υ'')→A1π1(υ') transition by using three wavelengths (main laser beam λ00=420.96 nm; two repumping laser beams λ10=443.00 nm and λ21=448.94 nm). The Doppler temperature (TDoppler=44.94 μK) and recoiltemperature(TRecoil=3.73 μK) for the A1π1 (υ'=0)X1Σ+0+ (υ''=0) transition are also calculated. These results can provide theoretical support for the experimental study of laser-cooled AlD molecules.

信阳师范学院学报：自然科学版Jan 1, 20210 citations