Measuring spin-rotation intervals in molecular cations is challenging, particularly so when the ions do not have electric-dipole-allowed rovibrational transitions. We present a method, based on an angular-momentum basis transformation, to determine the spin-rotational fine structure of molecular ions from the fine structure of high Rydberg states. The method is illustrated by the determination of the so far unknown spin-rotation fine structure of the fundamentally important He_{2}^{+} ion in the X ^{2}Σ_{u}^{+} state. The fine-structure splittings of the v^{+}=0, N^{+}=1, 3, and 5 levels of He_{2}^{+} are 7.96(14), 17.91(32), and 28.0(6) MHz, respectively. The experiment relies on the use of single-mode cw radiation to record spectra of high Rydberg states of He_{2} from the a ^{3}Σ_{u}^{+} metastable state.
We use a multistage Zeeman decelerator to generate slow beams ($v\ensuremath{\simeq}100\phantom{\rule{0.16em}{0ex}}\mathrm{m}/\mathrm{s}$) of translationally cold, spin-polarized metastable $a\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Sigma}}_{u}^{+}\phantom{\rule{4pt}{0ex}}{\mathrm{He}}_{2}$ molecules and perform a precision measurement of their spin-rotation fine structure. The spin polarization results from the elimination of the high-field-seeking
J=N spin-rotational component of each rotational level (rotational quantum number
N) by the Zeeman deceleration process. By repopulating the
J=N component from the $J=N\ifmmode\pm\else\textpm\fi{}1$ low-field-seeking components using radio-frequency radiation, we measured the spin-rotation fine structure of 13 rovibrational levels with
v=0, 1 and
N=1–21. The low beam velocity and the resulting long interaction times with the radio-frequency radiation were exploited to determine the transition frequencies with a precision of 300 Hz.
The fine structure of high-angular-momentum
n=9 and 10 Rydberg states of barium has been measured precisely, using the resonant excitation Stark ionization spectroscopy method. Optical transitions corresponding to $(n,{n}^{\ensuremath{'}})=(10,30)$, (9,17), and (9,20) were induced with a Doppler-tuned
CO2 laser, determining the fine-structure energies corresponding to all
n=9 and 10 levels with $L\ensuremath{\geqslant}6$. The pattern of these fine-structure energies conforms closely with an effective potential model, by comparison with which the dipole and quadrupole polarizabilities of
Ba+ can be determined. Combining our data with earlier measurements made it possible to deduce, in addition, the portion of ${\ensuremath{\alpha}}_{2}$ due to the lowest excited
D state of
Ba+. Our best estimates of these three properties are ${\ensuremath{\alpha}}_{1}=124.30(16){a}_{0}^{3}$, ${\ensuremath{\alpha}}_{2}=2462(361){a}_{0}^{5}$, and ${\ensuremath{\alpha}}_{2}^{0}=1828(88){a}_{0}^{5}$.
Electric-dipole forbidden spectroscopic transitions in atoms form the basis of many advanced implementations of quantum computers, atomic clocks and quantum sensors. Coherently addressing such transitions in molecules which are among the most ubiquitous and versatile quantum objects has remained a long-standing challenge owing to their complex energy-level structure. Here, we report the search, observation and coherent manipulation of electric-quadrupole rotational-vibrational transitions in single trapped molecules using a quantum-logic-spectroscopy protocol. We identified individual hyperfine-Zeeman-rotational components of the fundamental vibrational transition of the nitrogen molecular ion, N
2+, and performed coherent population transfer between energy levels. Our work opens up new perspectives for precision molecular spectroscopy, for high-fidelity qubits encoded in the rotational-vibrational motion of molecules, for precise infrared molecular clocks and for searches for new physics
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.
We report rovibronic spectra of the A
3Σ+(
v′=0−2) - X
3ΠΩ(v=0) rovibronic transitions (
∣Ω∣=0,1 and 2) of the CO
2+ doubly-charged molecular ion. Spectra were recorded at high resolution (
∼5~cm
−1) in a fast beam of CO
2+ molecules by detecting the Coulomb explosion of the molecules upon excitation to the A state. Measurements were guided by \textit{ab initio} calculations which then assisted the assignment of the observed spectral features. Our results resolve the spin-orbit splittings of the ground vibronic state X
3ΠΩ(v=0), but not the rotational structure of the bands due to spectral congestion, and provide spectroscopic information on CO
2+ with unprecedented resolution. In doing so they expand our knowledge of this benchmark doubly charged molecular ion and expand the short list of doubly charged molecules studied at high resolution.
\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.30]{maby_ortho_h2-01.eps} \end{wrapfigure} We use high Rydberg states to measure the properties of H
2+ and HD
+ in the vicinity of their dissociation limits H
++H, H
++D and H+D
+, with particular emphasis on quasibound rovibrational levels above the dissociation threshold of the X
+ 2Σg+ ground state. Although the existence of these quasibound levels has been predicted a long time ago, they have never been observed. Positions and widths of the lowest resonances have not been calculated either. Given the role that such states play in the three-body and radiative recombination of H(1s) and H
+ to form H
2+, this lack of data may be regarded as one of the largest unknown aspects of this otherwise accurately known fundamental molecular cation. We present measurements of the positions and widths of the lowest-lying quasibound rotational levels (shape resonances) of H
2+, located close to the top of the centrifugal barriers and which decay by quantum-mechanical tunneling. For HD
+ we present measurements of rovibrational levels of the A
+ 2Σu+ state, located between the two dissociation limits. Because of the g-u-symmetry breaking in HD
+, these levels are coupled to the H
++D continuum by nonadiabatic interactions (Feshbach resonances). The experimental results will be compared with the positions and widths we calculate for these levels using a potential model for the X
+ and the A
+ state of H
2+ and HD
+ which includes adiabatic, nonadiabatic, relativistic and radiative corrections to the Born-Oppenheimer potential energies.