Theoretical High-resolution Spectroscopy Beyond Ccsd(t): The Interstellar Anions Cn−, Cch−, C3n−, And C4h−

Using extended coupled cluster methods well beyond fc-CCSD(T), spectroscopic properties of several molecular anions of astrochemical interest have been calculated. Excellent agreement with MW data is observed for CN$^{-}$, CCH$^{-}$, C$_{3}$N$^{-}$, and C$_{4}$H$^{-}$ and accurate equilibrium structures are presented for all four species. The results for CCH$^{-}$ are superior to recent theoretical results of Huang and Lee\footnote{X.~Huang, T.~J.~Lee \textit{J.~Chem.~Phys.} \textbf{2009}, {\textit{131}}, 104301.} and confirm the quality of our earlier predictions.\footnote{M.~Mladenovi\'{c}, P.~Botschwina, P.~Sebald, S.~Carter, \textit{Theor.~Chem.~Acc.} \textbf{1998}, \textit{100}, 134.} The new calculations predict $\nu_1$ = 3209.3~cm$^{-1}$, $\nu_2$~(band origin) = 510.0~cm$^{-1}$, and $\nu_3$ = 1804.4~cm$^{-1}$, estimated errors not exceeding 1~cm$^{-1}$

Rovibrational States Of Hbf+ And Hco+ Isotopologues Up To High J: Theory And Experiment

Near-equilibrium potential energy surfaces for HBF$^+$ and HCO$^+$, obtained from high-level calculations beyond fc-CCSD(T), are employed in variational calculations for many rovibrational states of various isotopologues. Calculated effective spectroscopic parameters are in excellent agreement with available experimental data and many predictions are being made, also for line intensities of HBF$^+$ and HCO$^+$ isotopologues. Combining a difference frequency system with glow discharge and a discharge modulation scheme, six and seven lines of the $\nu_1$ bands for H$^{11}$BF$^+$ and H$^{10}$BF$^+$, respectively, were observed. Together with data obtained from microwave spectroscopy, the spectroscopic constants of the $\nu_1$ states could be derived through least-squares fitting

Highly Accurate Quantum-chemical Calculations For The Interstellar Molecules C3 And L-c3h+

Composite potential energy surfaces with coupled-cluster contributions up to CCSDTQP were constructed for C$_3$ and l-C$_3$H$^+$ and used in the calculation of spectroscopic properties. The use of very large AO basis sets and the consideration of higher-order correlation beyond CCSD(T) is of utmost importance for C$_3$ in order to arrive at quantitative spectroscopic data. The first detection of l-C$_3$H$^+$ in the interstellar medium was reported by Pety et al.,\footnote{J. Pety, P. Gratier, V. Guzm\'{a}n, E. Roueff, M. Gerin et al., \textit{Astron. Astrophys.} \textbf{2012}, \textit{A68}, 1-8.} who attributed 9 radio lines observed in the horsehead photodissociation region to that species. That assignment was questioned by the recent theoretical work of Huang et al.\footnote{X. Huang, R. C. Fortenberry, T. J. Lee, \textit{Astrophys. J. Lett.} \textbf{2013}, \textit{768:L25}, 1-5.} However, our more accurate calculations are well in support of the original assignment. The calculated ground-state rotational constant is $B_0 = 11248$~MHz, only $0.03\%$ off from the radio astronomical value of $11244.9512\pm0.0015$~MHz. The ratio of centrifugal distortion constants D$_0$(exp.)/D$_e$(theor.) of 1.8 is quite large, but reasonable in comparison with C$_3$O\footnote{P. Botschwina, R. Oswald, \textit{J. Chem. Phys.} \textbf{2008}, \textit{129}, 044305.} and C$_3$

Complexes of an argon atom with linear cations: results of coupled cluster calculations

Large-scale coupled cluster calculations have been carried out for complexes between an argon atom and four different linear cations (HCNH+, HC3NH+, HCCH+, and HC4H+). The two former closed-shell species have hydrogen-bonded linear forms, with nitrogen acting as proton donor, as the energetically most stable isomers. Their dissociation energies (D-0) are predicted to be 1261 and 1051 cm(-1), respectively. For Ar... HCCH+, the T-form with (2)A(1) symmetry is the absolute energy minimum of the potential energy surface, lying 1228 cm(-1) below the fragments at infinite separation. Ar... HC4H+ has a dissociation energy less than half as large and slightly prefers the linear structure. Various spectroscopic properties are predicted for the closed-shell complexes under investigation. (C) 2003 Elsevier Science (USA). All rights reserved

On the vibrations of linear C-11: A coupled cluster study

The near equilibrium potential energy surface and the harmonic vibrations of linear C, I have been studied by CCSD(T) calculations with large basis sets. In agreement with matrix IR spectroscopy, large intensities are calculated for the antisymmetric stretching vibrations nu(7) and nu(8). The wavenumber of the former band is predicted to have an unusually large anharmonicity contribution. Wavenumber shifts and changes in IR intensities arising from C-13 substitution are discussed in detail. Linear C, I exhibits no sign of floppiness and appears to behave like a fairly normal semi-rigid molecule. (c) 2006 Elsevier B.V. All rights reserved

Matrix isolation IR spectroscopic and ab initio studies of C(3)N(-) and related species

Coupled cluster calculations were carried out for C(3)N(-), CCNC(-), C(3)N, CCNC, C(3)N(+), and C(3)O. They support the experimental identification of the C(3)N(-) ion by means of matrix isolation infrared (IR) spectroscopy. The anion was generated in electric discharges through the cyanoacetylene isotopomers HC(3) (14)N, HC(3)(15)N, and (2)HC(3)N, trapped in cryogenic rare gas matrices (Ne, Ar, Kr), and detected via its two most intense IR absorption bands, assigned to the nu(1) and nu(2) stretching vibrations. C(3)N(-) appears to be quite a stable anion, with a vertical detachment energy predicted to be as high as 4.42 eV. A large equilibrium electric dipole moment of 3.10 D facilitates the investigation of C(3)N(-) by microwave spectroscopy and radio astronomy. Various structural parameters and spectroscopic properties have been calculated for all tetra-atomic species considered. (c) 2008 American Institute of Physics

Weak interactions in ion-ligand complexes of C3H3+ isomers: competition between H-bound and C-bound structures in c-C3H3+center dot L and H2CCCH+center dot L (L = Ne, Ar, N-2, CO2, and O-2)

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Explicitly correlated coupled cluster theory at the CCSD(T)-F12x level (T. B. Adler, G. Knizia, and H.-J. Werner, J. Chem. Phys.127, 221106, 2007) has been employed to study structures and vibrations of complexes of type c-C3H+3·L and H2C3H+·L (L = Ne, Ar, N2, CO2, and O2). Both cations have different binding sites, allowing for the formation of weak to moderately strong hydrogen bonds as well as “C-bound” or “π-bound” structures. In contrast to previous expectations, the energetically most favourable structures of all H2C3H+·L complexes investigated are “C-bound”, with the ligand bound to the methylenic carbon atom. The theoretical predictions enable a more detailed interpretation of infrared photodissociation (IRPD) spectra than was possible hitherto. In particular, the bands observed in the range 3238–3245 cm−1 (D. Roth and O. Dopfer, Phys. Chem. Chem. Phys.4, 4855, 2002) are assigned to essentially free acetylenic CH stretching vibrations of the propargyl cation in “C-bound” H2C3H+·L complexes

Calculated spectroscopic properties of HgH2

International audienceAbstract Ab initio calculations of the coupled cluster and spin-orbit configuration type, in conjunction with a small-core pseudopotential for the mercury atom, have been employed to construct near-equilibrium potential energy and electric dipole moment functions for HgH2. On that basis, rovibrational term energies and wavefunctions as well as transition dipole moments, absolute IR intensities and Einstein coefficients of spontaneous emission have been calculated variationally. Throughout, excellent agreement is obtained with recent experimental data from Fourier-transform infrared emission spectroscopy (A. Shayesteh, S. Yu , P. F. Bernath, J. Phys. Chem. A, 109, 10280 (2005)). The gas-phase wavenumbers of the symmetric stretching and the bending vibrations of 202HgH2 and 202HgD2 (in parentheses) are predicted to be 2012.3 (1442.8) cm-1 and 784.3 (564.1) cm-1, respectively. Various predictions are made for 202HgHD, for which no high-resolution spectra have yet been published