The states 1^1\Sigma^+_u, 1^1\Pi_u and 2^1\Sigma^+_u of Sr_2 studied by Fourier-transform spectroscopy

A high resolution study of the electronic states 1^1\Sigma^+_u and 1^1\Pi_u which belong to the asymptote 4^1D + 5^1S and of the state 2(A)^1\Sigma^+_u, which correlates to the asymptote 5^1P + 5^1S, is performed by Fourier-transform spectroscopy of fluorescence progressions induced by single frequency laser excitation. Precise descriptions of the potentials up to 2000 cm^{-1} above the bottom are derived and compared to currently available ab initio calculations. Especially for the state 1^1\Sigma^+_u large deviations are found. Rather weak and local perturbations are observed for the states 1^1\Pi_u and 2^1\Sigma^+_u, while a strong coupling of the state 1^1\Sigma^+_u to the component \Omega=0^+_u of the state 1^3\Pi_u, which belongs to the asymptote 5^3P + 5^1S, is indicated.Comment: Typing errors corrected (including numbers in table IX), 12 pages, 9 figure

Fourier-transform spectroscopy of Sr2 and revised ground state potential

Precise potentials for the ground state X1Sigma+g and the minimum region of the excited state 2_1Sigma+u of Sr2 are derived by high resolution Fourier-transform spectroscopy of fluorescence progressions from single frequency laser excitation of Sr2 produced in a heat pipe at 950 Celsius. A change of the rotational assignment by four units compared to an earlier work (G. Gerber, R. M\"oller, and H. Schneider, J. Chem. Phys. 81, 1538 (1984)) is needed for a consistent description leading to a significant shift of the potentials towards longer inter atomic distances. The huge amount of ground state data derived for the three different isotopomers 88Sr2, 86Sr88Sr and 87Sr88Sr (almost 60% of all excisting bound rovibrational ground state levels for the isotopomer 88Sr2) fixes this assignment undoubtedly. The presented ground state potential is derived from the observed transitions for the radial region from 4 to 11 A (9 cm-1 below the asymptote) and is extended to the longe range region by the use of theoretical dispersion coefficients together with already available photoassociation data. New estimations of the scattering lengths for the complete set of isotopic combinations are derived by mass scaling with the derived potential. The data set for the excited state 2_1Sigma+u was sufficient to derive a potential energy curve around the minimum.Comment: 10 pages, 7 figures, some small corrections done especially to the potential description of the excited state (already included in the published journal version

The coupled system (2)2Σ+ and (1)2Π of 7Li88Sr

We analyse rovibrational transitions of the (2)2Σ+-X(1)2Σ+ system of LiSr and find the energy levels of the (2)2Σ+ state to be perturbed by coupling between the (2)2Σ+ and (1)2Π states. We present an analysis of the coupled system yielding molecular parameters for the lowest vibrational levels of the (2)2Σ+ state and for higher vibrational levels of the (1)2Π state together with molecular coupling constants. Improved Dunham coefficients for the rovibrational levels of the X(1)2Σ+ state are also obtained, where the correlation with the parameters of the excited states is removed completely. © 2020 The Author(s). Published by IOP Publishing Ltd

Study of coupled states for the (4s^{2})^{1}S + (4s4p)^{3}P asymptote of Ca_{2}

The coupled states A^{1}\Sigma_{u}^{+} (^{1}D +}1}S), c^{3}\Pi_{u} (^{3}P + ^{1}S) and a^{3}\Sigma_{u}^{+} (^{3}P +}1}S) of the calcium dimer are investigated in a laser induced fluorescence experiment combined with high-resolution Fourier-transform spectroscopy. A global deperturbation analysis of the observed levels, considering a model, which is complete within the subspace of relevant neighboring states, is performed using the Fourier Grid Hamiltonian method. We determine the potential energy curve of the A^{1}\Sigma_{u}^{+} and c^{3}\Pi_{u} states and the strengths of the couplings between them. The c^{3}\Pi_{u} and \as states are of particular importance for the description of collisional processes between calcium atoms in the ground state ^{1}S_{0} and excited state ^{3}P_{1} applied in studies for establishing an optical frequency standard with Ca.Comment: 15 pages, 12 figure

The potential of the ground state of NaRb

The X$^{1}\Sigma ^{+}$ state of NaRb was studied by Fourier transform spectroscopy. An accurate potential energy curve was derived from more than 8800 transitions in isotopomers $^{23}$Na$^{85}$Rb and $^{23}$Na$^{87}$Rb. This potential reproduces the experimental observations within their uncertainties of 0.003 \rcm to 0.007 \rcm. The outer classical turning point of the last observed energy level ($v''=76$, $J''=27$) lies at $\approx 12.4$ \AA, leading to a energy of 4.5 \rcm below the ground state asymptote.Comment: 8 pages, 6 figures and 2 table

The X1Σ+^1\Sigma^+ and a3Σ+^3\Sigma^+ states of LiCs studied by Fourier-transform spectroscopy

We present the first high-resolution spectroscopic study of LiCs. LiCs is formed in a heat pipe oven and studied via laser-induced fluorescence Fourier-transform spectroscopy. By exciting molecules through the X$^1\Sigma^+$-B$^1\Pi$ and X$^1\Sigma^+$-D$^1\Pi$ transitions vibrational levels of the X$^1\Sigma^+$ ground state have been observed up to 3cm^{-1} below the dissociation limit enabling an accurate construction of the potential. Furthermore, rovibrational levels in the a$^3\Sigma^+$ triplet ground state have been observed because the excited states obtain sufficient triplet character at the corresponding excited atomic asymptote. With the help of coupled channels calculations accurate singlet and triplet ground state potentials were derived reaching the atomic ground state asymptote and allowing first predictions of cold collision properties of Li + Cs pairs.Comment: 10 pages, 5 figures. Submitted for publicatio

Spectroscopy of the a^3\Sigma_u^+ state and the coupling to the X^1\Sigma_g^+ state of K_2

We report on high resolution Fourier-transform spectroscopy of fluorescence to the a^3\Sigma_u^+ state excited by two-photon or two-step excitation from the X^1\Sigma_g^+ state to the 2^3\Pi_g state in the molecule K_2. These spectroscopic data are combined with recent results of Feshbach resonances and two-color photoassociation spectra for deriving the potential curves of X^1\Sigma_g^+ and a^3\Sigma_u^+ up to the asymptote. The precise relative position of the triplet levels with respect of the singlet levels was achieved by including the excitation energies from the X^1\Sigma_g^+ state to the 2^3\Pi_g state and down to the a^3\Sigma_u^+ state in the simultaneous fit of both potentials. The derived precise potential curves allow for reliable modeling of cold collisions of pairs of potassium atoms in their ^2S ground state

Formation of ultracold LiCs molecules

We present the first observation of ultracold LiCs molecules. The molecules are formed in a two-species magneto-optical trap and detected by two-photon ionization and time-of-flight mass spectrometry. The production rate coefficient is found to be in the range 10^{-18}\unit{cm^3s^{-1}} to 10^{-16}\unit{cm^3s^{-1}}, at least an order of magnitude smaller than for other heteronuclear diatomic molecules directly formed in a magneto-optical trap.Comment: 8 pages, 2 figure