The introduction of the concept of gradient force and scattering and absorption force is an important milestone in optical trapping. However the profiles of these forces are usually unknown, even for standard setups. Here, we successfully calculated them analytically via multipole expansion and numerically via Mie theory and fast Fourier transform. The former provides physical insight, while the latter is highly accurate and efficient. A recipe to create truly conservative energy landscapes is presented. These may open up qualitatively new features in optical manipulation.

We report on the production of ultracold heteronuclear YbLi* molecules in a dual-species magneto-optical trap by photoassociation (PA). The formation of the electronically excited molecules close to dissociation was observed by trap loss spectroscopy. We find 4 rovibrational states within a range of $250\mathrm{GHz}$ below the $\mathrm{Yb}\left({}^{1}S_0\right)+\mathrm{Li}\left({}^{2}P_{1/2}\right)$ asymptote and observe isotopic PA line shifts in mixtures of ${}^6\mathrm{Li}$ with ${}^{174}\mathrm{Yb}$, ${}^{172}\mathrm{Yb}$, and ${}^{176}\mathrm{Yb}$. We also describe our theoretical ab initio calculation for the relevant electronic potentials and utilize it to analyze and identify the lines in the experimentally observed spectrum.

Intense femtosecond infrared (IR) laser pulses have been used in recent years to study the breakup dynamics of molecules. However, observables such as kinetic energy release and branching ratios of molecular fragments are often difficult to predict by theory, making information of the molecular dynamics difficult to retrieve. In this work, we develop a simple model for sequential double ionization of molecules based on a density-matrix approach. The model describes tunneling ionization of the neutral and the ion as well as laser couplings between the ionic states simultaneously. Population of different doubly charged states can be obtained at a low computational cost. We applied our model to ${\mathrm{N}}_2$ and obtained a good agreement on the kinetic energy release spectrum with a previous experiment. This theoretical development could open up the opportunities to use intense short IR laser pulses with coincidence measurement to probe molecular dynamics.

We present a simple and general coherence model for multiorbital tunnel ionization of molecules, which we incorporate into our previously developed density-matrix approach for sequential double ionization [C. H. Yuen and C. D. Lin, Phys. Rev. A 106, 023120 (2022)]. The influence of this coherence is investigated through simulations of single ionization and sequential double ionization of ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ using few-cycle near-infrared laser pulses. In the case of single ionization, our results reveal the crucial role played by this coherence in generating population inversion in $\mathrm{N}{{}_2}^{+}$, suggesting a potential mechanism for air lasing. Regarding sequential double ionization, we observe only minor changes in the kinetic energy release spectra when the coherence is included, while noticeable differences in the angle-dependent dication yield for both ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ are found. Based on these findings, we recommend the inclusion of multiorbital tunnel ionization coherence in models for single ionization of general molecules, while suggesting that it can be safely neglected in the case of sequential double ionization.

Formamide is a potentially important molecule in the context of pre-biotic chemistry, since reactions involving it can lead to precursors of genetic and metabolic molecules. Being abundant in cometary material and in star-forming regions, the formation and destruction routes of interstellar formamide have been the focus of several studies. In this work, we focus on the electron recombination of protonated formamide, an important step of its destruction routes, by performing rigorous ab initio calculations of this process. We found that our values are in good agreement with previous qualitative estimates of the global rate coefficients. On the contrary, we propose a substantial revision of the products and branching ratios. Finally, we justify and emphasize the importance of carrying out similar theoretical calculations on the largest possible number of complex species of astrochemical interest.