We study ultracold long-range collisions of heteronuclear alkali-metal dimers with a reservoir gas of alkali-metal Rydberg atoms in a two-photon laser excitation scheme. In a low density regime where molecules remain outside the Rydberg orbits of the
reservoir atoms, we show that the two-photon photoassociation (PA) of the atom-molecule pair into a long-range bound trimer state is efficient over a broad range of atomic Rydberg channels. As a case study, we obtain the PA lineshapes for the formation of trimers composed of KRb molecules in the rovibrational ground state and excited Rb atoms in the asymptotic Rydberg levels $n^{2}S_j$ and $n^{2}D_j$, for $n=20-80$. We predict atom-molecule binding energies in the range $10-10^3$ kHz for the first vibrational state below threshold. The average trimer formation rate is order $10^8, {rm s}^{-1}$ at 1.0 $mu$K, and depends weakly on the principal quantum number $n$. Our results set the foundations for a broader understanding of exotic long range collisions of dilute molecules in ultracold atomic Rydberg reservoirs.
Absorbing UV radiation, ozone protects life on Earth and plays a fundamental role in Earths temperature balance. The formation of ozone occurs through the ternary recombination reaction: O$_2$+O+M $rightarrow$ O$_3$+M, where M can be N$_2$, O$_2$ or
Ar. Here, we developed a theoretical approach capable of modeling the formation of ozone molecules in ternary collisions, and applied it to the reaction with M=Ar because of extensive experimental data available. The rate coefficients for the direct formation of O$_3$ in ternary collisions O+O$_2$+Ar were computed for the first time as a function of collision energy, and thermally-averaged coefficients were derived for temperatures 5-900~K leading to a good agreement with available experimental data for temperatures 100-900~K. The present study shows that the formation of ozone in ternary collisions O+O$_2$+Ar at temperatures below 200~K proceeds through a formation of a temporary complex ArO$_2$, while at temperatures above 1000~K, the reaction proceeds mainly through a formation of long-lived vibrational resonances of O$_3^*$. At intermediate temperatures 200~K-1000~K, the process cannot be viewed as a two-step mechanism. In addition, it is found that the majority of O$_3$ molecules formed initially are weakly bound.
Coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] has been extensively employed as the reference method in benchmarking different quantum chemistry methods. In this work, we test the accuracy of CCSD(T) calculating gr
ound state electric dipole moments at the extrapolated complete basis set (CBS) limit. The calculated dipole moments have been compared to an experimental dataset consisted of diatomic molecules with various kinds of bond natures and spin configurations. As a result, to reach a satisfactory agreement with experimental dipole moments, core-correlations should be included for some molecules. However, even when core-correlations are included, the predicted dipole moment deviates considerably from the experimental values for molecules involving transition metal atoms.
We study the van der Waals interaction between Rydberg alkali-metal atoms with fine structure ($n^2L_j$; $Lleq 2$) and heteronuclear alkali-metal dimers in the ground rovibrational state ($X^1Sigma^+$; $v=0$, $J=0$). We compute the associated $C_6$ d
ispersion coefficients of atom-molecule pairs involving $^{133}$Cs and $^{85}$Rb atoms interacting with KRb, LiCs, LiRb, and RbCs molecules. The obtained dispersion coefficients can be accurately fitted to a state-dependent polynomial $O(n^7)$ over the range of principal quantum numbers $40leq nleq 150$. For all atom-molecule pairs considered, Rydberg states $n^2S_j$ and $n^2P_j$ result in attractive $1/R^6$ potentials. In contrast, $n^2D_j$ states can give rise to repulsive potentials for specific atom-molecule pairs. The interaction energy at the LeRoy distance approximately scales as $n^{-5}$ for $n>40$. For intermediate values of $nlesssim40$, both repulsive and attractive interaction energies in the order of $ 10-100 ,mu$K can be achieved with specific atomic and molecular species. The accuracy of the reported $C_6$ coefficients is limited by the quality of the atomic quantum defects, with relative errors $Delta C_6/C_6$ estimated to be no greater than 1% on average.
We have observed short-range photoassociation of LiRb to the two lowest vibrational states of the $d,^3Pi$ potential. These $d,^3Pi$ molecules then spontaneously decay to vibrational levels of the $a^3,Sigma^+$ state with generation rates of $sim10^3
$ molecules per second. This is the first observation of many of these $a,^3Sigma^+$ levels. We observe an alternation of the peak heights in the rotational photoassociation spectrum that suggests a $p$-wave shape resonance in the scattering state. Franck-Condon overlap calculations predict that photoassociation to higher vibrational levels of the $d,^3Pi$, in particular the sixth vibrational level, should populate the lowest vibrational level of the $a,^3Sigma^+$ state with a rate as high as $10^4$ molecules per second. These results encourage further work to explain our observed LiRb collisional physics using PECs. This work also motivates an experimental search for short-range photoassociation to other bound molecules, such as the $c,^3Sigma^+$ or $b,^3Pi$, as prospects for preparing ground-state molecules.
