Enthalpies of formation for C3O, HC3O+, C3S, and HC3S+ have been determined using an extended HEAT (High-accuracy Extrapolated Ab initio Thermochemistry) protocol. Special attention has been paid to estimating conservative 95% confidence intervals and the uncertainties in HEAT estimates for molecules containing a second-row element. The recommended values (gas phase, 298.15 K, 1 bar) are as follows: ΔfH298.15°(C3O) = 337.8 ± 1.6 kJ mol-1, ΔfH298.15°(HC3O+) = 1004.0 ± 1.3 kJ mol-1, ΔfH298.15°(C3S) = 583.6 ±3.1 kJ mol-1, and ΔfH298.15°(HC3S+) = 1192.2 ± 2.6 kJ mol-1. The corresponding proton affinities (gas phase, 1 bar) at T = 0 K amount to 857.9 ± 0.6 and 916.0 ± 0.8 kJ mol-1 for C3O and C3S and at T = 298.15 K to 864.0 ± 0.6 and 921.9 ± 0.8 kJ mol-1 for C3O and C3S, respectively. The calculated values align with the available data from the ATcT (Active Thermochemical Tables) analysis and some previous experimental and computational results. However, the uncertainties associated with the extended HEAT values presented here are significantly smaller.

Ethyl phosphaethyne, C2H5CP, has been characterized spectroscopically in the gas phase for the first time, employing millimeter- and submillimeter-wave spectroscopy in the frequency regime from 75 to 760 GHz. Spectroscopic detection and analysis was guided by high-level quantum-chemical calculations of molecular structures and force fields performed at the coupled-cluster singles and doubles level extended by a perturbative correction for the contribution from triple excitations, CCSD(T), in combination with large basis sets. Besides the parent isotopologue, the three singly substituted 13C species were observed in natural abundance up to frequencies as high as 500 GHz. Despite the comparably low astronomical abundance of phosphorus, phosphaalkynes, R-CP, such as C2H5CP are promising candidates for future radio astronomical detection.

The rotationally resolved infrared (IR) spectrum of the He-H3 + complex has been measured in a cryogenic ion trap experiment at a nominal temperature of 4 K. Predissociation of the stored complex has been invoked by excitation of the degenerate ν2 mode of the H3 + sub-unit using a pulsed optical parametric oscillator system. An assignment of the experimental spectrum became possible through one-to-one correlations with bands of the spectrum theoretically predicted in Paper I [Harding et al., J. Chem. Phys. 156, 144307 (2022)]. 19 bands have been assigned and analyzed, and the energy term diagram of the lower states of this floppy molecular complex has been derived from combination differences (CDs) in the experimental spectrum. Ground state combination differences (GSCDs) reveal a large part of the energy term diagram for the He-H3 + complex in its vibrational ground state, v = 0. Experimental and theoretical term energies agree within experimental accuracy for the rotational fine structure associated with the total angular momentum quantum number J and the parity e/f as well as for the coarse spacing of the lowest K states of the complex. This favorable comparison shows that the potential energy surface (PES) calculated in Paper I is accurate. The barriers between the three equivalent global minima in this PES are relatively low and the He-H3 + complex is extremely floppy, with nearly unhindered internal rotation of the H3 + sub-unit. The resulting Coriolis interactions couple the internal and end-over-end rotation of the complex and contribute significantly to the energy terms. They are observed both in experiment and theory and are, e.g., the origin of different rotational constants for states of e and f parity. Also in this respect, experiment and theory agree very well. Despite the assignment and analysis of many bands of the extremely rich IR spectrum of He-H3 +, higher levels of excitation, including the complex stretching mode, need further attention.

The direct random-phase approximation (dRPA) is used to calculate and compare atomization energies for the HEAT set and ten selected molecules of the G2-1 set using both plane waves and Gaussian-type orbitals. We describe detailed procedures to obtain highly accurate and well converged results for the projector augmented-wave method as implemented in the Vienna Ab initio Simulation Package as well as the explicitly correlated dRPA-F12 method as implemented in the TURBOMOLE package. The two approaches agree within chemical accuracy (1 kcal/mol) for the atomization energies of all considered molecules, both for the exact exchange as well as for the RPA. The root mean-square deviation is 0.41 kcal/mol for the exact exchange (evaluated using density functional theory orbitals) and 0.33 kcal/mol for exact exchange plus correlation from the RPA.

With a He-H3+ interaction potential obtained from advanced electronic structure calculations, we computed the vibration-rotation-tunneling (VRT) states of this complex for total angular momenta J from 0 to 9, both for the vibrational ground state and for the twofold degenerate v2 = 1 excited state of H3+. The potential has three equivalent global minima with depth De = 455.3 cm-1 for He in the plane of H3+, three equatorial saddle points that separate these minima with barriers of 159.5 cm-1, and two axial saddle points with energies of 243.1 cm-1 above the minima. The dissociation energies calculated for the complexes of He with ortho-H3+ (oH3+) and para-H3+ (pH3+) are D0 = 234.5 and 236.3 cm-1, respectively. Wave function plots of the VRT states show that they may be characterized as weakly hindered internal rotor states, delocalized over the three minima in the potential and with considerable amplitude at the barriers. Most of them are dominated by the jk = 10 and 11 rotational ground states of oH3+ and pH3+, with the intermolecular stretching mode excited up to v = 4 inclusive. However, we also found excited internal rotor states: 33 in He-oH3+, and 22 and 21 in He-pH3+. The VRT levels and wave functions were used to calculate the frequencies and line strengths of all allowed v2 = 0 → 1 rovibrational transitions in the complex. Theoretical spectra generated with these results are compared with the experimental spectra in Paper II [Salomon et al., J. Chem. Phys. 156, 144308 (2022)] and are extremely helpful in assigning these spectra. This comparison shows that the theoretical energy levels and spectra agree very well with the measured ones, which confirms the high accuracy of our ab initio He-H3+ interaction potential and of the ensuing calculations of the VRT states.

Infrared action spectra of the protonated forms of two fundamental organic nitriles, vinyl cyanide, C2H3CN, and ethyl cyanide, C2H5CN, have been observed using the FELion 22-pole ion trap apparatus and the Free Electron Laser for Infrared eXperiments (FELIX) at Radboud University, Nijmegen (The Netherlands). Vibrational bands of both ions were observed in the wavenumber regime between 300 and 2500 cm(-1) and spectroscopically assigned based on results from anharmonic force field calculations performed here at the coupled cluster level of theory. As the action spectroscopy scheme used in the present study probes the Ne-tagged weakly bound complexes, C2H3CNH+-Ne and C2H5CNH+-Ne, corresponding quantum-chemical calculations of these systems were also performed. Significant blueshifts observed for the strong-CNH+ bending modes indicate that the neon atom is attached to the proton bound to the nitrile group in both molecular ions.

The influence of long-range interactions on the structure of complexes of Eu(III) with four 9-hydroxy-phenalen-1-one ligands (HPLN) and one alkaline earth metal dication [Eu(PLN)4AE]+ (AE: Mg, Ca, Sr, and Ba) is analyzed. Through the [Eu(PLN)4Ca]+ complex, which is a charged complex with two metals-one of them a lanthanoid-and with four relatively fluxional π-ligands, the difficulties of describing such systems are identified. The inclusion of the D3(BJ) or D4 corrections to different density functionals introduces significant changes in the structure, which are shown to stem from the interaction between pairs of PLN ligands. This interaction is studied further with a variety of density functionals, wave-function based methods, and by means of the random phase approximation. By comparing the computed results with those from experimental evidence of gas-phase photoluminescence and ion mobility measurements it is concluded that the inclusion of dispersion corrections does not always yield structures that are in agreement with the experimental findings.

Huge efforts have recently been taken in the derivation of accurate compilations of rovibrational energies of water, one of the most important reference systems in spectroscopy. Such precision is desirable for all water isotopologues, although their investigation is challenged by hyperfine effects in their spectra. Frequency-comb locked noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS) allows for achieving high sensitivity, resolution, and accuracy. This technique has been employed to resolve the subtle hyperfine splittings of rovibrational transitions of H217O in the near-infrared region. Simulation and interpretation of the H217O saturation spectra have been supported by coupled-cluster calculations performed with large basis sets and accounting for high-level corrections. Experimental 17O hyperfine parameters are found in excellent agreement with the corresponding computed values. The need of including small hyperfine effects in the analysis of H217O spectra has been demonstrated together with the ability of the computational strategy employed for providing quantitative predictions of the corresponding parameters.

Following-up on our recent infrared photodissociation (IRPD) spectroscopic detection of the linear Ne-tagged HC 3 O + molecular ion, a the C-H stretching mode ν 1 of bare HC 3 O + has now been studied at high spectral resolution.The spectrum was observed using a 4 K cryogenic ion trap apparatus at Cologne (COLtrap) and a cw optical parametric oscillator using the method of laser-induced inhibition of complex growth (LIICG) with helium as tagging agent.Fifteen rotational-vibrational transitions were observed, covering P (8) to R( 6).The band origin is found at 3237.1 cm -1 and hence blueshifted by some 5 cm -1 compared to that of the HC 3 O + -Ne weakly bound complex probed earlier in the IRPD study.

The high resolution vibrational spectrum of vinyl acetylene (C2H3CCH) has been investigated in the far infrared region from 180 to 360 cm(-1) using the Bruker IFS 120 HR spectrometer at Justus-Liebig-Universitat, GieEen, Germany. The two energetically lowest vibrational fundamentals nu(13) and nu(18) at 214 cm(-1) and 304 cm(-1), respectively, were measured at a resolution of 0.0016 cm(-1). In addition to the fundamental modes, several hot bands originating from either nu(13) or nu(18) were observed and analyzed. The spectroscopic analysis was supported by high-level quantum-chemical coupled-cluster calculations and also made use of the Automated Spectral Line Assignment Procedure, ASAP, outlined earlier (MartinDrumel et al., 2015). In addition to the infrared study, so far unpublished millimeter-wave vibrational satellites that were measured in the course of an earlier study of the pure rotational spectrum of vinyl acetylene in its ground vibrational state (Thorwirth and Lichau, 2003) were added to the data set and are reported here for the first time. (C) 2021 Elsevier Inc. All rights reserved.

Spectroscopy is a powerful tool for studying molecules and is commonly performed on large thermal molecular ensembles that are perturbed by motional shifts and interactions with the environment and one another, resulting in convoluted spectra and limited resolution. Here, we use quantum-logic techniques to prepare a trapped molecular ion in a single quantum state, drive terahertz rotational transitions with an optical frequency comb, and read out the final state nondestructively, leaving the molecule ready for further manipulation. We can resolve rotational transitions to 11 significant digits and derive the rotational constant of 40CaH+ to be BR = 142 501 777.9(1.7) kilohertz. Our approach is suited for a wide range of molecular ions, including polyatomics and species relevant for tests of fundamental physics, chemistry, and astrophysics.

An up-to-date overview of the CFOUR program system is given. After providing a brief outline of the evolution of the program since its inception in 1989, a comprehensive presentation is given of its well-known capabilities for high-level coupled-cluster theory and its application to molecular properties. Subsequent to this generally well-known background information, much of the remaining content focuses on lesser-known capabilities of CFOUR, most of which have become available to the public only recently or will become available in the near future. Each of these new features is illustrated by a representative example, with additional discussion targeted to educating users as to classes of applications that are now enabled by these capabilities. Finally, some speculation about future directions is given, and the mode of distribution and support for CFOUR are outlined.

THOMAS SALOMON, OSKAR ASVANY, I. Physikalisches Institut, Universität zu Köln, Köln, Germany; DIETER GERLICH, Institut für Physik, Technische Universität Chemnitz, Chemnitz, Germany; IGOR SAVIC, Department of Physics, University of Novi Sad, Novi Sad, Serbia; AD VAN DER AVOIRD, Institute for Molecules and Materials (IMM), Radboud University Nijmegen, Nijmegen, Netherlands; MICHAEL E. HARDING, Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe, Germany; FILIPPO LIPPARINI, Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Pisa, Italy; JÜRGEN GAUSS, Institut für Physikalische Chemie, Universität Mainz, Mainz, Germany; STEPHAN SCHLEMMER, I. Physikalisches Institut, Universität zu Köln, Köln, Germany.

TURBOMOLE is a collaborative, multi-national software development project aiming to provide highly efficient and stable computational tools for quantum chemical simulations of molecules, clusters, periodic systems, and solutions. The TURBOMOLE software suite is optimized for widely available, inexpensive, and resource-efficient hardware such as multi-core workstations and small computer clusters. TURBOMOLE specializes in electronic structure methods with outstanding accuracy–cost ratio, such as density functional theory including local hybrids and the random phase approximation (RPA), GW-Bethe–Salpeter methods, second-order Møller–Plesset theory, and explicitly correlated coupled-cluster methods. TURBOMOLE is based on Gaussian basis sets and has been pivotal for the development of many fast and low-scaling algorithms in the past three decades, such as integral-direct methods, fast multipole methods, the resolution-of-the-identity approximation, imaginary frequency integration, Laplace transform, and pair natural orbital methods. This review focuses on recent additions to TURBOMOLE’s functionality, including excited-state methods, RPA and Green’s function methods, relativistic approaches, high-order molecular properties, solvation effects, and periodic systems. A variety of illustrative applications along with accuracy and timing data are discussed. Moreover, available interfaces to users as well as other software are summarized. TURBOMOLE’s current licensing, distribution, and support model are discussed, and an overview of TURBOMOLE’s development workflow is provided. Challenges such as communication and outreach, software infrastructure, and funding are highlighted.

The carbon chain ions HC_3O^+ and HC_3S^+ - longer variants of the famous "X-ogen" line carrier HCO^+ - have been observed for the first time using two cryogenic 22-pole ion trap apparatus (FELion, Coltrap) and two different light sources: the Free Electron Laser for Infrared eXperiments (FELIX), which was operated between 500 and 2500 cm^-1 and an optical parametric oscillator operating near 3200 cm^-1; signals from both experiments were detected by infrared predissociation action spectroscopy. The majority of vibrational fundamentals were observed for both ions and their vibrational wavenumbers compare very favorably with results from high-level anharmonic force field calculations performed here at the coupled-cluster level of theory. As the action spectroscopic scheme probes the Ne-tagged weakly bound variants, Ne-HC_3O^+ and Ne-HC_3S^+, corresponding calculations of these systems were also performed. Differences in the structures and molecular force fields between the bare ions and their Ne-tagged complexes are found to be very small.

The site-specific first microsolvation step of furan and some of its derivatives with methanol is explored to benchmark the ability of quantum-chemical methods to describe the structure, energetics, and vibrational spectrum at low temperature. Infrared and microwave spectra in supersonic jet expansions are used to quantify the docking preference and some relevant quantum states of the model complexes. Microwave spectroscopy strictly rules out in-plane docking of methanol as opposed to the top coordination of the aromatic ring. Contrasting comparison strategies, which emphasize either the experimental or the theoretical input, are explored. Within the harmonic approximation, only a few composite computational approaches are able to achieve a satisfactory performance. Deuteration experiments suggest that the harmonic treatment itself is largely justified for the zero-point energy, likely and by design due to the systematic cancellation of important anharmonic contributions between the docking variants. Therefore, discrepancies between experiment and theory for the isomer abundance are tentatively assigned to electronic structure deficiencies, but uncertainties remain on the nuclear dynamics side. Attempts to include anharmonic contributions indicate that for systems of this size, a uniform treatment of anharmonicity with systematically improved performance is not yet in sight.

Very accurate transition frequencies of HC5N were determined between 5.3 and 21.4 GHz with a Fourier transform microwave spectrometer. The molecules were generated by passing a mixture of HC3N and C2H2 highly diluted in neon through a discharge valve followed by supersonic expansion into the Fabry-Perot cavity of the spectrometer. The accuracies of the data permitted us to improve the experimental 14N nuclear quadrupole coupling parameter considerably and the first experimental determination of the 14N nuclear spin-rotation parameter. The transition frequencies are also well suited to determine in astronomical observations the local speed of rest velocities in molecular clouds with high fidelity. The same setup was used to study HC7N, albeit with modest improvement of the experimental 14N nuclear quadrupole coupling parameter. Quantum chemical calculations were carried out to determine 14N nuclear quadrupole and spin-rotation coupling parameters of HC5N, HC7N, and related molecules. These calculations included evaluation of vibrational and relativistic corrections to the non-relativistic equilibrium quadrupole coupling parameters; their considerations improved the agreement between calculated and experimental values substantially.

Spectroscopy is a powerful tool for studying molecules and is commonly performed on large thermal molecular ensembles that are perturbed by motional shifts and interactions with the environment and one another, resulting in convoluted spectra and limited resolution. Here, we use generally applicable quantum-logic techniques to prepare a trapped molecular ion in a single quantum state, drive terahertz rotational transitions with an optical frequency comb, and read out the final state non-destructively, leaving the molecule ready for further manipulation. We resolve rotational transitions to 11 significant digits and derive the rotational constant of CaH+ to be B_R = 142501777.9(1.7) kHz. Our approach suits a wide range of molecular ions, including polyatomics and species relevant for tests of fundamental physics, chemistry, and astrophysics.

The UV-vis absorption and emission spectra of halogenated tetraazaperopyrenes (TAPPs) have been investigated employing second-order approximate coupled cluster (CC2) and (time-dependent) density functional theory (DFT). We have found that the qualitative estimates of (vertical) absorption and excitation energies are possible within a single particle picture based on frontier orbitals, but the single particle picture is not sufficient to achieve quantitative accuracy. Going from the single-particle picture to the many-particle picture improves the agreement with experimental results, but still no satisfying correlation of theory and experiment is obtained. The comparison of CC2- and DFT-based methods reveals that deviations from the experimental results cannot be explained by deficiencies of the electronic-structure methods but rather stem from neglecting vibrational effects. An agreement of theoretical results and experimental spectra is found for adiabatic excitation energies, which are given as energy differences of vibronic states, which are directly accessible using both theoretical and experimental methods. The most pronounced vibronic influence is found for the Stokes shifts, which are significantly overestimated by computing the vertical electronic transitions only. Based on the vibronic contributions, the small Stokes shift of the TAPP compounds can be explained by the temperature dependence of the vibrationally resolved UV-vis spectra.