Accurate $EF{}^1Σ^+_g-X{}^1Σ^+_g$ transition energies in molecular hydrogen were determined for transitions originating from levels with highly-excited vibrational quantum number, $v=11$, in the ground electronic state. Doppler-free two-photon spectroscopy was applied on vibrationally excited H$_2^*$, produced via the photodissociation of H$_2$S, yielding transition frequencies with accuracies of $45$ MHz or $0.0015$ cm$^{-1}$. An important improvement is the enhanced detection efficiency by resonant excitation to autoionizing $7pπ$ electronic Rydberg states, resulting in narrow transitions due to reduced ac-Stark effects. Using known $EF$ level energies, the level energies of $X(v=11, J=1,3-5)$ states are derived with accuracies of typically 0.002 cm$^{-1}$. These experimental values are in excellent agreement with, and are more accurate than the results obtained from the most advanced ab initio molecular theory calculations including relativistic and QED contributions.
In a recent experiment (N. Wagner et al., PNAS v103, p13279) on SF$_{6}$, a high-harmonic generating laser pulse is preceded by a pump pulse which stimulates Raman-active modes in the molecule. Varying the time delay between the two pulses modulates high harmonic intensity, with frequencies equal to the vibration frequencies of the Raman-active modes. We propose an explanation of this modulation as a quantum interference between competing pathways that occur via adjacent vibrational states of the molecule. The Raman and high harmonic processes act as beamsplitters, producing vibrational quantu…
We report observation of two-photon emission from coherently excited vibrational state of solid parahydrogen, known as one of quantum solids. The coherent state between the ground and the excited states is prepared by stimulated Raman scattering using two visible laser pulses. The two-photon emission is triggered by another mid-infrared laser pulse. The observed two-photon emission persists even when the trigger pulse is injected long after the excitation. The observed phenomenon is due to a long decoherence time of the vibrational states of solid parahydrogen, which is attributed to special n…
The H$_2$+H$_2$ system has long been considered as a benchmark system for ro-vibrational energy transfer in bimolecular collisions. However, most studies thus far have focused on collisions involving H$_2$ molecules in the ground vibrational level or in the first excited vibrational state. While H$_2$+H$_2$/HD collisions have received wide attention due to the important role they play in astrophysics, D$_2$+D$_2$ collisions have received much less attention. Recently, Zhou et al. [Nat. Chem. 4 658 (2022)] examined stereodynamic aspects of rotational energy transfer in collisions of two aligned…
Photoexcitation rates for creation of ultralong-range Rydberg molecules (ULRM) with 31$\lesssim n \lesssim41$ in both ground and excited vibrational levels in cold ($T\sim900$~nK) gases of polarized and unpolarized $^{87}$Sr are presented. The measured production rates of the $ν=0, 1$ and 2 vibrational levels reveal rather different $n$ dependences which are analyzed by evaluating the Franck-Condon factors associated with excitation of the different vibrational levels and molecular rotational states. In particular, for gases of spin-polarized fermions, only Rydberg dimers with odd rotational q…
State-by-state cross sections for dissociative electron attachment and electron-impact dissociation for molecular oxygen are computed using ab initio resonance curves calculated with the R-matrix method. When O2 is in its vibrational ground state, the main contribution for both processes comes from the $^2Π_u$ resonance state of $O_2^-$ but with a significant contribution from the $^4Σ$ resonant state. Vibrational excitation leads to an increased contribution from the low-lying $^2Π_{g}$ resonance, greatly increased cross sections for both processes, and the threshold moving to lower energies.…
The article presents calculated dissociative recombination (DR) rate coefficients for H+3 . The previous theoretical work on H+3 was performed using the adiabatic hyperspherical approximation to calculate the target ion vibrational states and it considered just a limited number of ionic rotational states. In this study, we use accurate vibrational wave functions and a larger number of possible rotational states of the H3+ ground vibrational level. The DR rate coefficient obtained is found to agree better with the experimental data from storage-ring experiments than the previous theoretical cal…
Electron-impact cross sections for the dissociation process of vibrationally excited He2+ molecular ion, as a function of the incident electron energy are calculated for the dissociative transition X2Σ+u \to A2Σ+g by using the R-matrix method in the adiabatic-nuclei approximation. The potential energy curves for the involved electronic states and target properties, also calculated with the R-matrix method, were found to be in good agreement with the results reported in literature.
The possibility of electron attachment to the valence $^{3}Π$ state of CO is examined using an {\it ab initio} bound-state multireference configuration interaction approach. The resulting resonance has $^{4}Σ^{-}$ symmetry; the higher vibrational levels of this resonance state coincide with, or are nearly coincident with, levels of the parent $a^{3}Π$ state. Collisional relaxation to the lowest vibrational levels in hot plasma situations might yield the possibility of a long-lived CO$^-$ state.
We present a method to measure the decay rate of the first excited vibrational state of simple polar molecular ions being part of a Coulomb crystal in a cryogenic linear Paul trap. Specifically, we have monitored the decay of the $|ν$=$1,J$=$1 \rangle_X$ towards the $|ν$=$0,J$=$0 \rangle_X$ level in MgH$^+$ by saturated laser excitation of the $|ν$=$0,J$=$2 \rangle_X$-$|ν$=$1,J$=$1 \rangle_X$ transition followed by state selective resonance enhanced two-photon dissociation out of the $|ν$=$0,J$=$2 \rangle_X$ level. The technique enables the determination of decay rates, and thus absorption str…
We show that coherence between two excited ro-vibrational states belonging to the same molecular electronic configuration arises quite naturally due to their interaction with electromagnetic vacuum. For initial preparation of a molecule in the desired ro-vibrational states, we propose to employ the method of ultracold photoassociation. Spontaneous decay of the excited molecule then gives rise to vacuum induced coherence between the excited ro-vibrational states. We demonstrate theoretically an interesting interplay of effects due to vacuum induced coherence and photoassociation. We apply our t…
Triatomic molecule RaOH combines the advantages of laser-coolability and the spectrum with close opposite-parity doublets. This makes it a promising candidate for experimental study of the $\mathcal{P}$,$\mathcal{T}$-violation. Previous studies concentrated on the calculations for different geometries without the averaging over the rovibrational wave function and stressed the possibility that the dependence of the $\mathcal{P}$, $\mathcal{T}$ parameters on the bond angle may significantly alter the observed value. We obtain the rovibrational wave functions of RaOH in the ground electronic stat…
Since their first experimental observation, ultralong-range Rydberg molecules consisting of a highly excited Rydberg atom and a ground state atom have attracted the interest in the field of ultracold chemistry. Especially the intriguing properties like size, polarizability and type of binding they inherit from the Rydberg atom are of interest. An open question in the field is the reduced lifetime of the molecules compared to the corresponding atomic Rydberg states. In this letter we present an experimental study on the lifetimes of the ^3Σ(5s-35s) molecule in its vibrational ground state and i…
Starting from an ultracold sample of ground-state $^{23}$Na$^{87}$Rb molecules, we investigate the lowest ro-vibrational level of the $b^3Π$ state with high resolution laser spectroscopy. This electronic spin-forbidden $X^1Σ^+ \leftrightarrow b^3Π$ transition features a nearly diagonal Franck-Condon factor and has been proposed useful for probing and manipulating the ultracold molecular gas. We measure the transition strength directly by probing the ac Stark shift induced by near resonance light and determine the total excited-state spontaneous emission rate by observing the loss of molecules.…
We report on photoassociation spectroscopy probing the $c^3Σ_{1}^+$ potential of the bi-alkali NaCs molecule, identifying eleven vibrational lines between $v' = 0$ and $v' = 25$ of the excited $c^3Σ_{1}^+$ potential, and resolving their rotational and hyperfine structure. The observed lines are assigned by fitting to an effective Hamiltonian model of the excited state structure with rotational and hyperfine constants as free parameters. We discuss unexpected broadening of select vibrational lines, and its possible link to strong spin-orbit coupling of the $c^3Σ_{1}^+$ potential with the nearby…
We calculate the potential energy curves, the permanent dipole moment curves, and the lifetimes of the ground and excited vibrational states of the heteronuclear alkali dimers XY (X, Y = Li, Na, K, Rb, Cs) in the X1Σ+ electronic state using the coupled cluster with singles doubles and triples (CCSDT) method. All-electron quadruple-ζ basis sets with additional core functions are used for Li and Na, and small-core relativistic effective core potentials with quadruple-ζ quality basis sets are used for K, Rb and Cs. The inclusion of the coupled cluster non-perturbative triple excitations is shown …
We report a direct measurement of the 0-1 R(0) vibrational transition frequency in ground-state hydrogen deuteride (HD) using infrared-ultraviolet double resonance spectroscopy in a molecular beam. Ground-state molecules are vibrationally excited using a frequency comb referenced continuous-wave infrared laser, and the excited molecules are detected via state-selective ionization with a pulsed ultraviolet laser. We determine an absolute transition frequency of 111 448 815 477(13) kHz. The 0.12 parts-per-billion (ppb) uncertainty is limited primarily by the residual first-order Doppler shift.
We excite YbF molecules to low-lying vibrational levels of the $A^2Π_{1/2}$ state, and of the nearby perturber state sometimes called [18.6]0.5. By dispersing the fluorescence, we measure branching ratios for the radiative decay to vibrational levels of the $X^2Σ^+$ state. These ratios help to determine the optimum laser cooling scheme for the molecule. Our results establish the practicality of a scheme that was previously suggested [Tarbutt et al., New J. Phys. 15 (2013) 053034] and show how the scheme can be modified to provide a stronger radiative cooling force.
We consider two-color heteronuclear photoassociation of atoms into dipolar molecules in the J=1 electro-vibrational ground state, where a free-ground laser couples atoms directly to the ground state and a free-bound laser couples the atoms to an electronically-excited state. This problem raises an interest because heteronuclear photoassociation from atoms to near-ground state molecules is limited by the small size of the target state. Nevertheless, the addition of the excited state creates a second pathway for creating ground state molecules, leading to quantum interference between direct phot…
The ^1Σ^+ electronic ground states of MgLi^+ and CaLi^+ molecular ions are investigated for their spectroscopic constants and properties such as the dipole- and quadrupole moments, and static dipole polarizabilities. The quadrupole moments and the static dipole polarizabilities for these ions have been calculated and reported here, for the first time. The maximum possible error bars, arising due to the finite basis set and the exclusion of higher correlation effects beyond partial triples, are quoted for reliability. Further, the adiabatic effects such as diagonal Born-Oppenheimer corrections …
The transfer of weakly bound KRb molecules from levels just below the dissociation threshold into the vibrational ground state with shaped laser pulses is studied. Optimal control theory is employed to calculate the pulses. The complexity of modelling the molecular structure is successively increased in order to study the effects of the long-range behavior of the excited state potential, resonant spin-orbit coupling and singlet-triplet mixing.
We study the effect of a strong static homogeneous electric field on the highly excited rovibrational levels of the LiCs dimer in its electronic ground state. Our full rovibrational investigation of the system includes the interaction with the field due to the permanent electric dipole moment and the polarizability of the molecule. We explore the evolution of the states next to the dissociation threshold as the field strength is increased. The rotational and vibrational dynamics are influenced by the field; effects such as orientation, angular motion hybridization and squeezing of the vibratio…
High-precision variational calculations of the operators for the relativistic corrections in the leading $mα^4$ order are presented. The ro-vibrational states in the range of the total orbital angular momentum $L\!=\!0\!-\!4$ and vibrational quantum number $v\!=\!0\!-\!10$ for the $\mbox{H}_2^+$ and $\mbox{HD}^+$ molecular ions are considered. We estimate that about ten significant digits are obtained. This high precision is required for making theoretical predictions for transition frequencies at the level of $10^{-12}$ relative uncertainty.
Within the Franck-Condon approximation, the single ionization of H$_2$ leaves H$_2^+$ in a coherent superposition of 19 nuclear vibrational states. We numerically design an optimal laser pulse train to transfer such a coherent nuclear wave packet to the ground vibrational state of H$_2^+$. The simulation results show that the population of the ground state after the transfer is more than 91%. Frequency analysis of the designed optimal pulse reveals that the transfer principle is mainly an anti-Stokes transition, i.e., the H$_2^+$ in $1sσ_g$ with excited nuclear vibrational states is first pump…
We investigated transition strengths from ultracold weakly bound 41K87Rb molecules produced via the photoassociation of laser-cooled atoms. An accurate potential energy curve of the excited state (3)1Sigma+ was constructed by carrying out direct potential fit analysis of rotational spectra obtained via depletion spectroscopy. Vibrational energies and rotational constants extracted from the depletion spectra of v'=41-50 levels were combined with the results of the previous spectroscopic study, and they were used for modifying an ab initio potential. An accuracy of 0.14% in vibrational level spa…
The static and dynamic electric multipolar polarizabilities and second hyperpolarizabilities of the H$_2^+$, D$_2^+$, and HD$^+$ molecular ions in the ground and first excited states are calculated nonrelativistically using explicitly correlated Hylleraas basis sets. The calculations are fully nonadiabatic; the Born-Oppenheimer approximation is not used. Comparisons are made with published theoretical and experimental results, where available. In our approach, no derivatives of energy functions nor derivatives of response functions are needed. In particular, we make contact with earlier calcul…
The non-relativistic three-body Schrödinger equation of the heteronuclear molecular ion HD$^+$ is solved in perimetric coordinates using the Lagrange-mesh method. Energies and wave functions of the four lowest vibrational bound or quasibound states $v=0-3$ are calculated for total orbital momenta from 0 to 47. Energies are given with an accuracy from about 12 digits for the lowest vibrational level to at least 9 digits for the third vibrational excited level. With a simple calculation using the corresponding wave functions, accurate dipole transition probabilities per time unit between those l…
We present the results of an experimental and theoretical study of the electronically excited $\tripletex$ state of $^{87}$Rb$_2$ molecules. The vibrational energies are measured for deeply bound states from the bottom up to $v'=15$ using laser spectroscopy of ultracold Rb$_2$ Feshbach molecules. The spectrum of each vibrational state is dominated by a 47\,GHz splitting into a $\cog$ and $\clg$ component caused mainly by a strong second order spin-orbit interaction. Our spectroscopy fully resolves the rotational, hyperfine, and Zeeman structure of the spectrum. We are able to describe to first…
A new state of the H$_2^+$ molecular ion with binding energy of 1.09$\times10^{-9}$ a.u. below the first dissociation limit is predicted, using highly accurate numerical nonrelativistic quantum calculations. It is the first L=0 excited state, antisymmetric with respect to the exchange of the two protons. It manifests itself as a huge p-H scattering length of $a=750\pm 5$ Bohr radii.
