Having only three electrons, He₂⁺ represents a system for which highly accurate ab initio calculations are possible. The latest calculations of rovibrational energies in He₂⁺ do not include relativistic or QED corrections but claim an accuracy of 120 MHzW.-C. Tung, M. Pavanello and L. Adamowicz, J. Chem. Phys. 136, 104309 (2012). We have performed high-resolution Rydberg spectroscopy of metastable He₂ moleculesP. Jansen, L. Semeria, L. Esteban Hofer, S. Scheidegger, J.A. Agner, H. Schmutz, and F. Merkt, Phys. Rev. Lett. 115, 133202 (2015).nd employed multichannel-quantum-defect-theory extrapolation techniquesD. Sprecher, J. Liu, T. Krähenmann, M. Schäfer, and F. Merkt, J. Chem. Phys. 140, 064304 (2014).o determine the rotational energy-level structure in the He₂⁺ ion. To this end, we have produced samples of metastable helium molecules in supersonic beams with velocities tunable down to 100 m/s by combining a cryogenic supersonic-beam source with a multistage Zeeman deceleratorM. Motsch, P. Jansen, J. A. Agner, H. Schmutz, and F. Merkt, Phys. Rev. A 89, 043420 (2014). The metastable He₂ molecules are excited to np Rydberg states using the frequency-doubled output of a pulse-amplified ring dye laser. Although the bandwidth of the laser system is too large to observe the reduction of the Doppler width resulting from deceleration, the deceleration greatly simplifies the spectral assignments because of its spin-rotational state selectivity. Our approach enabled us to determine the rotational structure of He₂ with an unprecedented accuracy of 18 MHz, to quantify the size of the relativistic and QED corrections by comparison with the results of Tung et al. and to precisely measure the rotational structure of the metastable state for comparison with the results of Focsa et al.C. Focsa, P. F. Bernath, and R. Colin, J. Mol. Spectrosc. 191, 209 (1998). Here, we present an extension of these measurements in which we have measured higher rotational intervals of He₂⁺. In addition, we have replaced the pulsed UV laser by a cw UV laser and improved the resolution of the spectra by a factor of more than fiveP. Jansen, L. Semeria, and F. Merkt, J. Mol. Spectrosc. 322, 9 (2016). W.-C. Tung, M. Pavanello and L. Adamowicz, J. Chem. Phys. 136, 104309 (2012).. P. Jansen, L. Semeria, L. Esteban Hofer, S. Scheidegger, J.A. Agner, H. Schmutz, and F. Merkt, Phys. Rev. Lett. 115, 133202 (2015).a D. Sprecher, J. Liu, T. Krähenmann, M. Schäfer, and F. Merkt, J. Chem. Phys. 140, 064304 (2014).t M. Motsch, P. Jansen, J. A. Agner, H. Schmutz, and F. Merkt, Phys. Rev. A 89, 043420 (2014).. C. Focsa, P. F. Bernath, and R. Colin, J. Mol. Spectrosc. 191, 209 (1998).. P. Jansen, L. Semeria, and F. Merkt, J. Mol. Spectrosc. 322, 9 (2016)..

I will describe recent advances in understanding the influence of nanoscale structure on plasmon-mediated electron dynamics. Steady-state extinction spectra of plasmonic nanoparticle networks are accurately described using hybridization models reminiscent of molecular orbitals. We have extended these molecular-based descriptions to account for nanoparticle electron dynamics by quantifying the coherence dephasing times of collective inter-particle plasmon modes of single nanostructures. In particular, we demonstrate that interference between plasmon modes of different angular momenta leads to increased coherence times. These observations are consistent with a model based on superpositions of molecular-like electronic states. These fundamental studies are important for understanding the structure-photonic-function relationship of plasmonic nanoparticles. This is because the spectroscopically determined coherence times reflect mode quality factors, which determine achievable amplification factors of optical signals. These new insights are made possible by recent advances in single-nanoparticle/molecule spectroscopy based on interferometric nonlinear optical detection. I will describe how the generation of sequences of phase-locked femtosecond laser pulses (33mrad phase stability) and their integration to an optical microscope were critical for this research.

Methanol is a simple and intensively studied organic molecule possessing one large-amplitude torsional motion. It has, for nearly a century, been a favorite of researchers in many fields, e.g., instrument builders, for whom methanol is often the first molecule chosen for testing an improved or a newly built instrument (including HIFI, the Heterodyne Instrument for the Far Infrared on board the Herschel space mission); theorists and/or dynamicists studying the challenging effects of a large-amplitude motion coupling with small-amplitude motions to enhance intramolecular vibrational energy redistribution; astronomers who have elevated methanol to their #1 interstellar weed because of its rich and omnipresent spectrum in the interstellar garden, where it serves as a unique probe for diagnosing conditions in star-forming regions; astrochemists studying isotopic ratios as clues to the chemical evolution of the universe; and fundamentalists seeking possible time variation of the proton/electron mass ratio in the standard model; just to name a few. From high-resolution to high-precision spectroscopy, the large-amplitude internal rotation of the methyl top against its OH framework in methanol has never failed to produce new surprises in spectral regions from the microwave all the way to the near IR. The very recent observation of completely unexpected large methanol hyperfine splittings is a vivid testimonial that the large-amplitude torsional motion can still lead us to unexplored landscapes. This talk will focus on the complicated vibration-torsion-rotation energy networks and interactions deduced from high resolution spectra; our efforts to understand some of them using ab-initio-assisted approaches and the modeling of torsion-rotation and torsionally mediated spin-rotation hyperfine splittings in methanol. These topics represent one part of the much larger fascinating world inhabited by methanolics.

The increasing sensitivity offered by the new generation of radio astronomical receivers and radio telescopes (single dishes and radio interferometers) has provided an enormous impact in our capacity to study the molecular content of interstellar and circumstellar clouds. Astronomers face now the challenging problem of interpreting the thousands of lines detected in hot cores which arise from isotopologues and vibrationally excited states of most known molecules. Although all strong features have been already assigned to abundant species, many of the lines still pending to be assigned could arise from very abundant molecular species having low dipole moment and/or very large partition functions. The only way to address this problem in astrophysics is through a close collaboration between astrophysicists and laboratory spectroscopists. In this talk I am going to present the results obtained over the last 10 years in interpreting the line surveys of Orion gathered with the 30m IRAM radio telescope and with ALMA. The most recent molecule found in this cloud is methyl isocyanate, CH₃NCO, for which near 400 lines have been found in Orion^a in the 80-280 GHz domain. This molecule has an abundance only a factor 5-20 below that of the well-known species HNCO and CH₃CN. The molecule has been also found towards the giant cloud SgrB2^b in the galactic center. Finally, I will present the case of the submillimeter spectrum of the carbon-rich evolved star IRC+10216 in which we have recently found Si₂C with an abundance similar to SiC₂. Our recent ALMA observations in a narrow band of 20 GHz around 265 GHz show near 200 features corresponding to the J=3-2 transition of hot HCN (vibrational levels up to 11000 cm⁻¹). In addition to HCN lines, a forest of several hundreds of U lines dominates the spectrum. Most of these lines arise from molecules that condensate very quickly into dust grains^c. ___________________________________ ^aJ. Cernicharo, Z.Kisiel, B.Tercero, et al., A&A 587, L4 (2016). ^bD.T. Halfen, V.V.Ilyushin, L.Ziurys, ApJ 812, L5 (2015). ^cJ. Cernicharo, F. Daniel, A. Castro-Carrizo, et al., ApJ, 778, L25 (2015).