On the CH near-infrared spectrum: absolute transition frequencies and an improved spectroscopic network at the kHz accuracy level.

Lamb dips of twenty lines in the P, Q, and R branches of the ν + ν + ν vibrational band of CH, in the spectral window of 7125-7230 cm, have been measured using an upgraded comb-calibrated frequency-stabilized cavity ring-down spectrometer, designed for extensive sub-Doppler measurements. Due to the large number of carefully executed Lamb-dip experiments, and to the extrapolation of absolute frequencies to zero pressure in each case, the combined average uncertainty of the measured line-center positions is 15 kHz (5 × 10 cm) with a 2-σ confidence level. Selection of the twenty lines was based on the theory of spectroscopic networks (SN), ensuring that a large number of transitions, measured previously by precision-spectroscopy investigations, could be connected to the and principal components of the SN of CH.

Analysis of measured high-resolution doublet rovibronic spectra and related line lists of CH and OH.

Detailed understanding of the energy-level structure of the quantum states as well as of the rovibronic spectra of the ethylidyne (CH) and the hydroxyl (OH) radicals is mandatory for a multitude of modelling efforts within multiple chemical, combustion, astrophysical, and atmospheric environments. Accurate empirical rovibronic energy levels, with associated uncertainties, are reported for the low-lying doublet electronic states of CH and OH, using the Measured Active Rotational-Vibrational Energy Levels (MARVEL) algorithm. For CH, a total of 1521 empirical energy levels are determined in the primary spectroscopic network (SN) of the radical, corresponding to the following seven electronic states: X Π, A Δ, B Σ, C Σ, D Π, E Σ, and F Σ.

Structure, energetics, and spectroscopy of the chromophores of HHe+n, HHe+n, and He+n clusters and their deuterated isotopologues.

The linear molecular ions HHe, HHe+2, and He+3 are the central units (chromophores) of certain He-solvated complexes of the HHe+n, HHe+n, and He+n families, respectively. These are complexes which do exist, according to mass-spectrometry studies, up to very high values. Apparently, for some of the HHe+n and He+n complexes, the linear symmetric tetratomic HHe+2 and the diatomic He+2 cations, respectively, may also be the central units.

Nonadiabatic phenomena in molecular vibrational polaritons.

Nonadiabatic phenomena are investigated in the rovibrational motion of molecules confined in an infrared cavity. Conical intersections (CIs) between vibrational polaritons, similar to CIs between electronic polaritonic surfaces, are found. The spectral, topological, and dynamic properties of the vibrational polaritons show clear fingerprints of nonadiabatic couplings between molecular vibration, rotation, and the cavity photonic mode.

Spectroscopic signatures of HHe and HHe.

Using two different action spectroscopic techniques, a high-resolution quantum cascade laser operating around 1300 cm-1 and a cryogenic ion trap machine, the proton shuttle motion of the cations HHe2+ and HHe3+ has been probed at a nominal temperature of 4 K. For HHe3+, the loosely bound character of this complex allowed predissociation spectroscopy to be used, and the observed broad features point to a lifetime of a few ps in the vibrationally excited state. For He-H+-He, a fundamental linear molecule consisting of only three nuclei and four electrons, the method of laser-induced inhibition of complex growth (LIICG) enabled the measurement of three accurate rovibrational transitions, pinning down its molecular parameters for the first time.

Spectroscopic-network-assisted precision spectroscopy and its application to water.

Frequency combs and cavity-enhanced optical techniques have revolutionized molecular spectroscopy: their combination allows recording saturated Doppler-free lines with ultrahigh precision. Network theory, based on the generalized Ritz principle, offers a powerful tool for the intelligent design and validation of such precision-spectroscopy experiments and the subsequent derivation of accurate energy differences. As a proof of concept, 156 carefully-selected near-infrared transitions are detected for HO, a benchmark system of molecular spectroscopy, at kHz accuracy.

Robust field-dressed spectra of diatomics in an optical lattice.

The absorption spectra of the cold Na molecule dressed by a linearly polarized standing laser wave is investigated with a theoretical model incorporating translational, electronic, vibrational as well as rotational degrees of freedom. In such a situation a light-induced conical intersection (LICI) can be formed (J. Phys.

Infrared Signatures of the HHe and DHe ( = 3-6) Complexes.

Combination of a cryogenic ion-trap machine, operated at 4.7 K, with the free-electron-laser FELIX allows the first experimental characterization of the unusually bright antisymmetric stretch (ν) and π-bending (ν) fundamentals of the He-X-He (X = H, D) chromophore of the in situ prepared HHe and DHe ( = 3-6) complexes. The band origins obtained are fully supported by first-principles quantum-chemical computations, performed at the MP2, the CCSD(T), and occasionally the CCSDTQ levels employing extended basis sets.

Accurate empirical rovibrational energies and transitions of HO.

Several significant improvements are proposed to the computational molecular spectroscopy protocol MARVEL (Measured Active Rotational-Vibrational Energy Levels) facilitating the inversion of a large set of measured rovibrational transitions to energy levels. The most important algorithmic changes include the use of groups of transitions, blocked by their estimated experimental (source segment) uncertainties, an inversion and weighted least-squares refinement procedure based on sequential addition of blocks of decreasing accuracy, the introduction of spectroscopic cycles into the refinement process, automated recalibration, synchronization of the combination difference relations to reduce residual uncertainties in the resulting dataset of empirical (MARVEL) energy levels, and improved classification of the lines and energy levels based on their accuracy and dependability. The resulting protocol, through handling a large number of measurements of similar accuracy, retains, or even improves upon, the best reported uncertainties of the spectroscopic transitions employed.

Rovibrational Resonances in HHe.

The nuclear dynamics of the metastable HHe complex is explored by symmetry considerations and angular momentum addition rules as well as by accurate quantum chemical computations with complex coordinate scaling, complex absorbing potential, and stabilization techniques. About 200 long-lived rovibrational resonance states of the complex are characterized and selected long-lived states are analyzed in detail. The stabilization mechanism of these long-lived resonance states is discussed on the basis of probability density plots of the wave functions.

A general variational approach for computing rovibrational resonances of polyatomic molecules. Application to the weakly bound HHe and H⋅CO systems.

The quasi-variational quantum chemical protocol and code GENIUSH [E. Mátyus et al., J.

Rovibrational energy levels of the F(-)(H2O) and F(-)(D2O) complexes.

The variational nuclear-motion codes ElVibRot and GENIUSH have been used to compute rotational-vibrational states of the F(-)(H2O) anion and its deuterated isotopologue, F(-)(D2O), employing a full-dimensional, semiglobal potential energy surface (PES) called SLBCL, developed as part of this study for the ground electronic state of the complex. The PES is determined from all-electron, explicitly correlated coupled-cluster singles, doubles, and connected triples [CCSD(T)-F12a] computations with an atom-centered, fixed-exponent Gaussian basis set of cc-pCVTZ-F12 quality. The SLBCL PES accurately reproduces the two equivalent minima of the complex, the corresponding transition barrier of C2v point-group symmetry, as well as the proton transfer and the dissociation asymptotes towards the products HF + OH(-) and F(-) + H2O, respectively.