In this dissertation, three distinct but related experimental works are reported. The first is a study of the highly excited 3^1 Δ_g and 4^1 Δ_g electronic states of 85Rb2. Rovibrational levels of the two electronic states were probed using the high-resolution optical-optical double resonance (OODR) technique by exciting 85Rb2 molecules from thermally populated levels of the X(_ ^1)Σ_g^+ ground state through intermediate levels of the B^1 Π_u electronic state. The (_ ^1)Δ_g resonances induced by the probe laser were observed by detecting laser induced fluorescence (LIF) from nearby, collisionally populated triplet levels to the a^3 Σ_u^+ triplet ground state. The (_ ^1)Δ_g character of the two electronic states was confirmed by showing that the probe transitions to these states abide by (_ ^1)Δ←(_ ^1)Π dipole selection rules and by observing that their lowest rotational level is J = 2. A set of molecular constants and a Rydberg-Klein-Rees (RKR) potential energy curve (PEC) were calculated from the observed term values for each electronic state and compared with ab initio predictions. This is the first observation of (_ ^1)Δ_g states in Rb2.The next results are on the highly excited 6(_ ^3)Π_0g electronic state of the 133Cs2 molecule in an energetic region where very little is known. Rovibrational levels of the excited triplet state were experimentally observed by the perturbation-facilitated-OODR (PFOODR) using a level of the A(_ ^1)Σ_u^+ ~b(_ ^3)Π_u mixed manifold as an intermediate. A progression of P and R branch probe laser resonances were detected by measuring (LIF) to the a(_ ^3)Σ_u^+ state as a function of the probe laser frequency. For select rovibrational levels of the 6(_ ^3)Π_0g state, dispersed fluorescence to the a(_ ^3)Σ_u^+ state and the A(_ ^1)Σ_u^+ ~b(_ ^3)Π_u manifold were also recorded and compared with Frank-Condon factor (FCF) calculations to determine spin multiplicity and vibrational numbering. Term values of the 284 observed rovibrational levels and their quantum numbers were fit to a Dunham expansion to obtain molecular constants, which were in turn used to generate a corresponding RKR-PEC. Comparison to ab initio results led to the assignment of 6(_ ^3)Π_0g . Accurate and high-resolution potential energy curves for the excited states of alkali dimers are crucial for quantum control and cooling experiments relying on techniques such as Stimulated Raman adiabatic passage (STIRAP) and resonantly enhanced multiphoton ionization (REMPI).Lastly, the results of producing state selective molecular angular momentum orientation using dressed states created by a cw optical field are reported. The experiment was carried out with 7Li2 molecules and a combination of left- and right-hand circularly polarized lasers. Our approach exploits the dependence of the Rabi frequency on the quantum number M, which makes it possible to achieve complete M-state selectivity and thus molecular angular momentum orientation relative to laboratory frame space-fixed axes. Using molecules in a (_ ^1)Σ state, orientation of the rotational angular momentum, R ⃑, can be achieved by spectrally resolving the Autler-Townes split M components of the total angular momentum, J ⃑. Results of orienting J ⃑ in (_ ^1)Π state molecules are also discussed. This is the first time complete angular momentum orientation has been achieved in nonpolar molecules and should aid the efforts of stereochemistry, molecular imaging, photodissociation and photoassociation, to name a few.
This dissertation describes methods and results of spectroscopic studies of the NaCs molecule. NaCs is of particular interest in many labs where experimental studies of ultra-cold molecules are being conducted. Data obtained in the present work will also be useful as benchmarks for various theoretical calculations. Our goals in studying this molecule were to map out high lying electronic states and to understand how these states interact with one another. Sodium and cesium metal were heated in a heat-pipe oven to form a vapor of NaCs molecules. These molecules were excited using narrow band, continuous wave (cw), tunable lasers. We employed the optical-optical double resonance (OODR) technique to obtain Doppler-free spectra of transitions to rotational and vibrational levels of high lying electronic states. One state of particular interest was the 12(0+) electronic state. Rovibrational level energies corresponding to this state were measured and used to generate a potential energy curve using computer programs to implement both the Rydberg-Klein-Rees (RKR) method and the inverted perturbation approach (IPA). By observing fluorescence from the 12(0+) state resolved as a function of wavelength, we determined that this state interacts with the nearby 11(0+) electronic state, which was previously mapped out by Ashman et al. A two-stage coupling model was devised to describe the resolved fluorescence originating from these two interacting states. The electronic states interact via spin-orbit coupling, while the individual rovibrational levels interact via a second mechanism, likely nonadiabatic coupling. This two-stage coupling between the levels of these states causes quantum interference between fluorescence pathways associated with different components of the wavefunctions describing these levels. This interference results in more complicated resolved fluorescence spectra. The model was used to fit parameters describing these interactions so that the resolved fluorescence spectra could be reproduced. The NaCs 43 π electronic state was also studied in this work. Energies of many rovibrational levels belonging to the 43 π electronic state were measured. This state is interesting because it likely has a potential energy curve with a double minimum, which results in a different type of quantum interference, directly observed in resolved spectra. The state also very likely has interactions with the 11(0+) and 12(0+) states. Energies of many rovibrational levels lying above the energy of the barrier between the two minima were measured, and it appears that we also observed a few levels lying below the barrier. Since the laser wavelengths necessary to excite the lowest vibrational levels were not available, an experimental potential curve could not be produced. Therefore, rovibrational level energies and spectroscopic constants are tabulated.
In this thesis properties of ultracold alkali dimers are studied both theoretically and experimentally. In the first, theoretical, part, the prospects for the formation of ultracold LiCs dimers in deeply bound vibrational levels using photoassociation (PA) are investigated. Furthermore a previous systematic investigation of the structure of all alkali dimers is extended by the ab initio calculation of static dipole polarizabilities. An extensive comparison with other published results supports the reliability of the chosen method. Based on these results an experimental scheme for the creation of an sample of oriented ultracold dipolar molecules is developed. In the second, experimental part the formation of LiCs ground state molecules by PA is investigated. PA spectroscopy is used to improve the accuracy of the potential energy curve for the B1P and the value of the dissociation energy of the X1S+ state significantly. The rovibrational distribution of ground state molecules is probed in a combination of resonance-enhanced multi-photon ionization and depletion spectroscopy. A simple scheme is found to form ultracold polar LiCs molecules in the absolute ground state X1S+,v''=0,J''=0. In a quasi-electrostatic trap created by a CO2 laser, LiCs molecules are formed and stored. A lifetime of 24(3)s, limited by collisions with background gas, is observed and rate coefficients for inelastic collisions between LiCs in high vibrational states and Cs atoms are determined. The long storage time facilitates the observation of radiative decay of polar molecules towards lower vibrational levels.
High resolution Fourier transform spectra (FTS) of laser induced fluorescence (LIF) of $C\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+};D\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Pi}\ensuremath{\rightarrow}A\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}--b\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}$ and $A\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}--b\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}\ensuremath{\rightarrow}X\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}$ transitions in
Na85Rb and
Na87Rb were obtained. An analysis of the direct LIF spectra together with the rotational relaxation satellites provided highly accurate rovibronic term values for $(4\ensuremath{\leqslant}J\ensuremath{\leqslant}163)$ of the $A\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}--b\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}$ complex, covering about 1950 mostly singlet levels $0\ensuremath{\leqslant}{v}_{A}\ensuremath{\leqslant}49$ and a considerable number
(>360) of the predominantly triplet $b\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}_{0,1}$ sublevels. The direct deperturbation analysis of the singlet-triplet
A−−b complex was performed by means of the inverted channel-coupling approach with Hund's coupling case
a basis functions. The electronic matrix elements of the model $4\ifmmode\times\else\texttimes\fi{}4$ Hamiltonian were defined as piecewise analytical functions of the internuclear distance. Besides the Born-Oppenheimer potential energy curves of the mutually perturbed states and the off-diagonal spin-orbit (SO)
A−−b coupling function, the SO splitting of the $b\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}$ state was determined due to the pronounced electronic-rotation interaction between the $b\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}_{0}$ and $b\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}_{1}$ components observed for high
J levels. Overall, 24 mass-invariant fitting parameters have been required to reproduce about 2300 experimental term values of both isotopomers with a standard deviation of $0.012\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, which is consistent with the uncertainty of the FTS experiment. An analytical mapping procedure based on a reduced variable representation of the radial coordinate was used to diminish the computational effort for the uniform finite-difference grid solution of the coupled-channel equations. The derived nonadiabatic
A−−b wave functions were used to evaluate the $A\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}--b\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}--D\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Pi}$, $a\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Sigma}^{+}$, $X\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}$ rovibronic transition probabilities. The relative intensity distributions predicted for the $D\ensuremath{\rightarrow}A--b$ and $A--b\ensuremath{\rightarrow}X$ LIF progressions agree with their experimental counterparts within the accuracy of the measurements. The calculated
A−−b−−a,
X transition probabilities were applied for simulation of the stimulated Raman $a\ensuremath{\rightarrow}A--b\ensuremath{\rightarrow}X$ processes, which can lead to efficient formation of ultracold NaRb molecules in the ground level
vX=0;
JX=0.
I present spectroscopic data on ultracold lithium-rubidium molecules in a dual species magneto-optical-trap in order to find suitable intermediate states to transfer population to the rotational, vibrational and electronic ground state via a stimulated Raman process. First, I improved the accuracy of the energetic location of the ground state by two orders of magnitude using photoassociation as a spectroscopic tool to measure the energy of bound states relative to the scattering continuum. Second, we studied the d 3Π-D 1Π and A 1Σ+ -b 3Π0+ excited electronic manifolds with a combination of resonantly-enhancedmulti-photon-ionization and depletion spectroscopy finding suitable singlet-triplet mixed states to use in the Raman transfer scheme. Finally, I demonstrate robust optical phase locked loops to maintain the coherence between the two lasers required for the Raman process.
We report the formation of ultracold (7)Li(85)Rb molecules in the a(3)Σ(+) electronic state by photoassociation (PA) and their detection via resonantly enhanced multiphoton ionization (REMPI). With our dual-species Li and Rb magneto-optical trap apparatus, we detect PA resonances with binding energies up to ∼62 cm(-1) below the (7)Li 2s (2)S1/2 + (85)Rb 5p (2)P1/2 asymptote. In addition, we use REMPI spectroscopy to probe the a(3)Σ(+) state and excited electronic 3(3)Π and 4(3)Σ(+) states and identify a(3)Σ(+) (v″ = 7-13), 3(3)Π (vΠ' = 0-10), and 4(3)Σ(+) (vΣ' = 0-5) vibrational levels. Our line assignments agree well with ab initio calculations. These preliminary spectroscopic studies on previously unobserved electronic states are crucial to discovering transition pathways for transferring ultracold LiRb molecules created via PA to deeply bound rovibrational levels of the electronic ground state.