Accurate CHIPR Potential Energy Surface for the Lowest Triplet State of C₃

Abstract

We report the first global ab initio-based potential energy surface (PES) for ground-state triplet C3(3A′) based on accurate energies extrapolated to the complete basis set (CBS) limit, and using the combined-hyperbolic-inverse-power-representation method for the analytical modeling. By relying on a cost-effective CBS­(D,T) protocol, we ensure that the final form reproduces all topographical features of the PES, including its cyclic-linear isomerization barrier, with CBS­(5,6)-quality. To partially account for the incompleteness of the N-electron basis and other minor effects, the available accurate experimental data on the relevant diatomics were used to obtain direct-fit curves that replace the theoretical ones in the many-body expansion. Besides describing properly long-range interactions at all asymptotic channels and permutational symmetry by built-in construction, the PES reported here reproduces the proper exothermicities at dissociation regions as well as the spectroscopy of the diatomic fragments. Bound vibrational state calculations in both linear and cyclic isomers have also been carried out, unveiling a good match of the available data on C3(ã 3Πu), while assisting with IR band positions for C3(3A2 ′) that may serve as a guide for its laboratory and astronomical detection.

Theoretical studies of carbon isotopic fractionation in reactions of C with C2: dynamics, kinetics, and isotopologue equilibria

“…To obtain a balanced and accurate description of both valence and long-range features of the potentials, ab initio calculations were carried out at the multireference configuration interaction [MRCI(+Q)] level of theory (Szalay et al 2012), with the final total energies subsequently extrapolated to the complete (one-electron) basis set limit (Varandas 2018) prior to the fitting procedure. For the singlet PES, Rocha & Varandas (2018) improved the spectroscopy near its linear minima [ -C 3 (X 1 Σ + g )] by morphing this global form with an accurate Taylor-series expansion taken from Schröder & Sebald (2016) in this work have their ab initio two-body terms replaced by the direct-fit, experimentally determined, diatomic curves (Rocha & Varandas 2019). The spectroscopic attributes of the isotopically substituted dissociation channels and of the C 3 intermediates spanned by the trajectories are shown in Tables 1 and 2, respectively.…”

“…For the singlet PES, Rocha & Varandas (2018) improved the spectroscopy near its linear minima [ -C 3 (X 1 Σ + g )] by morphing this global form with an accurate Taylor-series expansion taken from Schröder & Se- bald (2016). In this spirit and to partially account for the incompleteness of the N-electron basis and other minor effects, both global PESs used in this work have their ab initio two-body terms replaced by the direct-fit, experimentally determined, diatomic curves (Rocha & Varandas 2019). The spectroscopic attributes of the isotopically substituted dissociation channels and of the C 3 intermediates spanned by the trajectories are shown in Tables 1 and 2, respectively.…”

“…As for the calculation of both forward and reverse rate coefficients of reactions (2)-( 5), we herein employ the quasiclassical trajectory (QCT) method (Truhlar & Muckerman 1979;Peslherbe et al 1999), with the previously obtained (nuclearmass-independent) global PESs of C 3 ( 3 A ) (Rocha & Varandas 2019) and C 3 ( 1 A ) (Rocha & Varandas 2018) dictating the interactions between the involved nuclei (see Sect. 2).…”

“…As for the calculation of both forward and reverse rate coefficients of reactions (2)-( 5), we herein employ the quasi-classical trajectory (QCT) method (Truhlar & Muckerman 1979;Peslherbe et al 1999), with the previously obtained (nuclear-massindependent) global PESs of C 3 ( 3 A ) (Rocha & Varandas 2019) and C 3 ( 1 A ) (Rocha & Varandas 2018) dictating the interactions between the involved nuclei (see Section 2). From the calculated rate coefficients as a function of T , equilibrium constants for these processes are also provided and their possible impact on the overall C isotopic fractionation chemistry is briefly discussed.…”

Long-range additive and nonadditive potentials in a hybrid system: Ground state atom, excited state atom, and ion

“…Detailed procedures for calculating and constructing potential energy surfaces (and other properties) of triatomic systems have been developed, exemplified (for the representative molecules discussed above) by recent works such as for tricarbon [36], for ozone [37][38][39], and for H 3 [40]. A successful strategy to construct three-atom potential energy surfaces using semi-empirical methods requires input calculations of atom-dimer and three-atom longrange potentials [41][42][43].…”