The application of two-color resonant four-wave mixing (TC-RFWM) in combination with a discharge slit-source in a molecular beam environment is advantageous for the study of perturbations in C₂. Initial investigations have shown the potential of the method by a detailed deperturbation of the \textd  ³Π_\textg, v=4 state.P. Bornhauser, G. Knopp, T. Gerber, and P.P. Radi, Journal of Molecular Spectroscopy 262, 69 (2010)he deperturbation of the \textd  ³Π_\textg, v=6 state unveiled the presence of the energetically lowest high-spin state of C₂. This dark state gains transition strength through the perturbation process with the \textd  ³Π_\textg, v=6 state yielding weak spectral features that are observable by the high sensitivity of the TC-RFWM technique. The successful deperturbation study of the \textd  ³Π_\textg, v=6 state resulted in the spectroscopic characterization of the quintet (\text1  ⁵Π_\textg) and an additional triplet state (\textb  ³Σ_\textg⁻, v=19). P. Bornhauser, Y. Sych, G. Knopp, T. Gerber, and P.P. Radi, Journal of Chemical Physics 134, 044302 (2011)ore recently, investigations have been performed by applying unfolded TC-RFWM to obtain further information on the quintet manifold. The first high-spin transition (\text1  ⁵Π_\textu- \text1  ⁵Π_\textg) has been observed via an intermediate "gateway" state exhibiting both substantial triplet and quintet character owing to the perturbation between the \text1  ⁵Π_\textg, v=0 and the \textd  ³Π_\textg, v=6 states. The high-lying quintet state is found to be predissociative and displays a shallow potential that accommodates three vibrational levels only. Bornhauser, P., Marquardt, R., Gourlaouen, C., Knopp, G., Beck, M., Gerber, T., van Bokhoven, JA, and Radi, P. P., Journal of Physical Chemistry, submittedurther studies of the high-spin system will be presented in this contribution. By applying TC-RFWM and laser-induced fluorescence, data on the vibrational structure of the \text1  ⁵Π_\textu- \text1  ⁵Π_\textg system is obtained. The results are combined with high-level ab initio computations at the multi-reference configuration interaction (MRCI) level of theory and the largest possible basis currently implemented in the 2012 version of MOLPRO.

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P. Bornhauser, G. Knopp, T. Gerber, and P.P. Radi, Journal of Molecular Spectroscopy 262, 69 (2010)T P. Bornhauser, Y. Sych, G. Knopp, T. Gerber, and P.P. Radi, Journal of Chemical Physics 134, 044302 (2011)M Bornhauser, P., Marquardt, R., Gourlaouen, C., Knopp, G., Beck, M., Gerber, T., van Bokhoven, JA, and Radi, P. P., Journal of Physical Chemistry, submittedF

In a recent series of combined experimental and theoretical studies we investigated the ground state and several excited states of the Rb-alkaline earth molecules RbSrF. Lackner, G. Krois, T. Buchsteiner, J. V. Pototschnig, and W. E. Ernst, Phys. Rev. Lett., 2014, 113, 153001; G. Krois, F. Lackner, J. V. Pototschnig, T. Buchsteiner, and W. E. Ernst, Phys. Chem. Chem. Phys., 2014, 16, 22373; J. V. Pototschnig, G. Krois, F. Lackner, and W. E. Ernst, J. Chem. Phys., 2014, 141, 234309nd RbCa.J. V. Pototschnig, G. Krois, F. Lackner, and W. E. Ernst, J. Mol. Spectrosc., in Press (2015), doi:10.1016/j.jms.2015.01.006he group of alkali-alkaline earth (AK-AKE) molecules has drawn attention for applications in ultracold molecular physics and the measurement of fundamental constantsM. Kajita, G. Gopakumar, M. Abe, and M. Hada, J. Mol. Spectrosc., 2014, 300, 99-107ue to their large permanent electric and magnetic dipole moments in the ground state. These properties should allow for an easy manipulation of the molecules and simulations of spin models in optical lattices.A. Micheli, G. K. Brennen, and P. Zoller, Nature Physics, 2006, 2, 341-347n our studies we found that the permanent electric dipole moment points in different directions for certain electronically excited states, and changes the sign in some cases as a function of bond length. We summarize our results, give possible causes for the measured trends in terms of molecular orbital theory and extrapolate the tendencies to other combinations of AK and AKE - elements. F. Lackner, G. Krois, T. Buchsteiner, J. V. Pototschnig, and W. E. Ernst, Phys. Rev. Lett., 2014, 113, 153001; G. Krois, F. Lackner, J. V. Pototschnig, T. Buchsteiner, and W. E. Ernst, Phys. Chem. Chem. Phys., 2014, 16, 22373; J. V. Pototschnig, G. Krois, F. Lackner, and W. E. Ernst, J. Chem. Phys., 2014, 141, 234309a J. V. Pototschnig, G. Krois, F. Lackner, and W. E. Ernst, J. Mol. Spectrosc., in Press (2015), doi:10.1016/j.jms.2015.01.006T M. Kajita, G. Gopakumar, M. Abe, and M. Hada, J. Mol. Spectrosc., 2014, 300, 99-107d A. Micheli, G. K. Brennen, and P. Zoller, Nature Physics, 2006, 2, 341-347I

The photodetachment spectrum of BeO⁻ has been studied for the first time using high resolution velocity map imaging photoelectron spectroscopy. Vibrational contours were imaged and compared with Franck-Condon simulations for the ground and excited states of the neutral. The first measured electron affinity of BeO, and anisotropies of several transitions were also measured. Experimental findings are compared to high level ab initio calculations.

The ¹Σ⁺← ¹Σ⁺ ground state to dipole bound state electronic transition of AlO⁻ has been studied with both rotationally resolved autodetachment spectroscopy and high resolution velocity map imaging photoelectron spectroscopy in a newly constructed apparatus. Vibrational and rotational molecular constants have been determined for both the ground state (ν^"= 0,1) and excited dipole bound state (ν^′= 0,1) of the aluminum monoxide anion. The spectra yield the electron binding energy of the dipole bound state, and a more accurate electron affinity for AlO. The photoelectron anisotropies of several transitions were measured. Experimental findings are compared to high level ab initio calculations. Additionally, high resolution photodetachment imaging of AlO^{− 1}Σ⁺ within energy ranges well above the detachment threshold were measured and compared to previous, low resolution photodetachment results.

The BaO⁺ cation is a promising candidate for studies conducted at ultra-cold temperatures. It is known that the ion can be formed by the reaction of laser-cooled Ba⁺ with N₂O or O₂. Spectroscopic data are now needed for the BaO⁺ cation, for both characterization of the internal state population distributions and the design of population transfer schemes. We have obtained the first spectroscopic data for BaO⁺ using the pulsed-field ionization, zero kinetic energy (PFI-ZEKE) photoelectron technique. Two-color ionization was carried out via the A¹Σ⁺-X¹Σ⁺ transition of BaO. Vibronic levels of the X²Σ⁺, A²Π_3/2 and A²Π_1/2 states of BaO⁺ have been characterized. The results are compared with the predictions of high-level electronic structure calculations.

Motivated by a diverse range of applications in physics and chemistry, currently there is great interest in the cooling of molecules to very low temperatures ( ≤ 1 mK). Direct laser cooling has been previously demonstrated for the diatomic radicals SrFE.S. Shuman, J.F. Barry and D. DeMille, Nature 467, 820 (2010)^,J.F. Barry, E.S. Shuman, E.B. Norrgard and D. DeMille, Phys. Rev. Lett. 108, 103002 (2012) YOM.T. Hummon, M. Yeo, B.K. Stuhl, A.L. Collopy, Y. Xia, and J. Ye, Phys. Rev. Lett. 110, 143001 (2013)^,M. Yeo, M.T. Hummon, A.L. Collopy, B. Yan, B. Hemmerling, E. Chae, J.M. Doyle, and J. Ye, arXiv:1501.04683 (2015) and CaFV. Zhelyazkova, A. Cournol, T.E. Wall, A. Matsushima, J.J. Hudson, E.A. Hinds, M.R. Tarbutt, and B.E. Sauer, Phys. Rev. A 89, 053416 (2014) and most recently a three-dimensional magneto-optical trap (MOT) of SrF molecules was achievedJ.F. Barry, D.J. McCarron, E.B. Norrgard, M.H. Steinecker and D. DeMille, Nature 512, 286 (2014)^,D.J. McCarron, E.B. Norrgard, M.H. Steinecker and D. DeMille, arXiv:1412.8220 (2014) To determine the possibility of laser cooling for polyatomic molecules containing three or more atoms, detailed information is required about their Franck−Condon factors (FCFs) for emission from the excited states of interest. Here we report on the high−resolution laser excitation spectra, recorded field−free and in the presence of a static magnetic field, and on the dispersed fluorescence (DF) spectra for the A^2_1/2 X^2^+ and B^2^+ X ^2^+ J.F. Barry, E.S. Shuman, E.B. Norrgard and D. DeMille, Phys. Rev. Lett. 108, 103002 (2012),M.T. Hummon, M. Yeo, B.K. Stuhl, A.L. Collopy, Y. Xia, and J. Ye, Phys. Rev. Lett. 110, 143001 (2013)D.J. McCarron, E.B. Norrgard, M.H. Steinecker and D. DeMille, arXiv:1412.8220 (2014).

Hydrocarbons such as ethylene (C₂H₄) and methane (CH₄) are of considerable interest for the modeling of planetary atmospheres and other astrophysical applications. Knowledge of rovibrational transitions of hydrocarbons is of primary importance in many fields but remains a formidable challenge for the theory and spectral analysis. Essentially two theoretical approaches for the computation and prediction of spectra exist. The first one is based on empirically-fitted effective spectroscopic models. Several databases aim at collecting the corresponding data but the information about C₂H₄ spectrum present in these databases remains limited, only some spectral ranges around 1000, 3000 and 6000 cm⁻¹ being available. Another way for computing energies, line positions and intensities is based on global variational calculations using ab initio surfaces. Although they do not yet reach the spectroscopic accuracy, they could provide reliable predictions which could be quantitatively accurate with respect to the precision of available observations and as complete as possible. All this thus requires extensive first-principles quantum mechanical calculations essentially based on two necessary ingredients: (i) accurate intramolecular potential energy surface and dipole moment surface components and (ii) efficient computational methods to achieve a good numerical convergence. We report predictions of vibrational and rovibrational energy levels of C₂H₄ using our new ground state potential energy surface obtained from extended ab initio calculationsT. Delahaye, A. V. Nikitin, M. Rey, P. G. Szalay, and Vl. G. Tyuterev, J. Chem. Phys. 2014, 141, 104301 Additionally we will introduce line positions and line intensities predictions based on a new dipole moment surface for ethylene. These results will be compared with previous works on ethylene and its isotopologues.

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T. Delahaye, A. V. Nikitin, M. Rey, P. G. Szalay, and Vl. G. Tyuterev, J. Chem. Phys. 2014, 141, 104301.

Naphthalene is one of the simple polycyclic aromatic molecule, and it is interesting that the excited state dynamics take place. To understand the excited state dynamics, rotationally resolved fluorescence excitation spectra of several vibronic bands were measured. K. Yoshida, Y. Semba, S. Kasahara, T. Yamanaka, and M. Baba, J. Chem. Phys. 130, 19304 (2009) H. Katô, M. Baba, and S. Kasahara, Bull. Chem. Soc. Jpn. 80, 456 (2007) In this work, we have measured high-resolution fluorescence excitation spectra across a single mode laser and molecular beam at light angle. Vibronic bands, which lies 2866 cm ⁻¹ and 3068 cm ⁻¹ above the 0-0 band (0⁰₀ + 2866 cm⁻¹ band and 0⁰₀ + 3068 cm⁻¹ band), were measured. Absolute wavenumber was calibrated with accuracy 0.0002 cm⁻¹ by the measurement of Doppler-free absorption spectrum of I₂ molecule and transmitting light intensity of the stabilized etalon. Rotational lines of the 0⁰₀ + 2866 cm⁻¹ band were almost resolved. A part of the rotational lines were assigned, and several energy shifts were found. On the other hand, rotational lines were not completely resolved for the 0⁰₀ + 3068 cm⁻¹ band.

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K. Yoshida, Y. Semba, S. Kasahara, T. Yamanaka, and M. Baba, J. Chem. Phys. 130, 19304 (2009)

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High-resolution fluorescence excitation spectra of the S₁ ← S₀ electronic transition have been observed for 1-Cl naphthalene (1-ClN) and 2-Cl naphthalene (2-ClN). Sub-Doppler excitation spectra were measured by crossing a single-mode UV laser beam perpendicular to a collimated molecular beam. The absolute wavenumber was calibrated with accuracy 0.0002 cm⁻¹ by measurement of the Doppler-free saturation spectrum of iodine molecule and fringe pattern of the stabilized etalon. For 2-ClN, the rotationally resolved high-resolution spectra were obtained for the 0⁰₀ and 0⁰₀+1042 cm⁻¹ bands, and these molecular constants were determined in high accuracy. The obtained molecular constants of the 0⁰₀ band are good agreement with the ones reported by Plusquellic et. al. D. F. Plusquellic, S. R. Davis, and F. Jahanmir, J. Chem. Phys., 115, 225 (2001).or the 0⁰₀+1042 cm⁻¹ band, the local energy shifts were found. On the other hand, for 1-ClN, the rotational lines were not fully resolved because the fluorescence lifetime is shorter than the one of 2-ClN. Then we determined the molecular constants of 1-ClN from the comparison the observed spectrum with calculated one.

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D. F. Plusquellic, S. R. Davis, and F. Jahanmir, J. Chem. Phys., 115, 225 (2001).F