Accurate ab initio quartic force fields of cyclic and bent HC2N isomers

Inostroza, Natalia; Huang, Xinchuan; Lee, Timothy J.

doi:doi:10.1063/1.3671389

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Theoretical characterization of intermolecular vibrational states through the multi-configuration time dependent Hartree approach: The He_2,3ICl clusters

Benchmark, full-dimensional calculations on the ground and excited vibrational states for the tetra-, and penta-atomic weakly bound He2,3ICl complexes are reported. The representation of the potential energy surfaces includes three-body HeICl potentials parameterized to coupled-cluster singles, doubles, and perturbative triples ab initio data. These terms are important in accurately describing the interactions of such highly floppy systems. The corresponding 6D/9D computations are performed with...

Nitrogen nucleation in a cryogenic supersonic nozzle

We follow the vapor–liquid phase transition of N2 in a cryogenic supersonic nozzle apparatus using static pressure measurements. Under our operating conditions, condensation always occurs well below the triple point. Mean field kinetic nucleation theory (MKNT) does a better job of predicting the conditions corresponding to the estimated maximum nucleation rates, Jmax = 1017±1 cm−3 s−1, than two variants of classical nucleation theory. Combining the current results with the nucleation pulse chamb...

Highly correlated ab initio quartic force fields (QFFs) are used to calculate the equilibrium structures and predict the spectroscopic parameters of three HC₂N isomers. Specifically, the ground state quasilinear triplet and the lowest cyclic and bent singlet isomers are included in the present study. Extensive treatment of correlation effects were included using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, denoted as CCSD(T). Dunning's correlation-consistent basis sets cc-pVXZ, X = 3,4,5, were used, and a three-point formula for extrapolation to the one-particle basis set limit was used. Core-correlation and scalar relativistic corrections were also included to yield highly accurate QFFs. The QFFs were used together with second-order perturbation theory (PT) (with proper treatment of Fermi resonances) and variational methods to solve the nuclear Schrödinger equation. The quasilinear nature of the triplet isomer is problematic, and it is concluded that a QFF is not adequate to describe properly all of the fundamental vibrational frequencies and spectroscopic constants (though some constants not dependent on the bending motion are well reproduced by PT). On the other hand, this procedure (a QFF together with either PT or variational methods) leads to highly accurate fundamental vibrational frequencies and spectroscopic constants for the cyclic and bent singlet isomers of HC₂N. All three isomers possess significant dipole moments, 3.05 D, 3.06 D, and 1.71 D, for the quasilinear triplet, the cyclic singlet, and the bent singlet isomers, respectively. It is concluded that the spectroscopic constants determined for the cyclic and bent singlet isomers are the most accurate available, and it is hoped that these will be useful in the interpretation of high-resolution astronomical observations or laboratory experiments.

Article Outline

INTRODUCTION
THEORY AND COMPUTATIONAL DETAILS
RESULTS AND DISCUSSIONS
1. Equilibrium structures, harmonic frequencies, and equilibrium rotational constants
2. Fundamental frequencies, effective rotational constants, and quartic and sextic centrifugal distortion constants
3. Force constants, anharmonic constants, and vibration–rotation interaction constants
4. Isomeric energy differences and dipole moments
CONCLUSIONS

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KEYWORDS and PACS

Keywords

ab initio calculations, correlation methods, coupled cluster calculations, extrapolation, ground states, hydrogen compounds, molecular moments, perturbation theory, relativistic corrections, Schrodinger equation, triplet state, variational techniques, vibrational states

PACS

31.15.bw

Coupled-cluster theory
31.15.aj

Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
33.20.Tp

Vibrational analysis
33.15.Kr

Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.xp

Perturbation theory
31.15.xt

Variational techniques

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.3671389

PUBLICATION DATA

ISSN

0021-9606 (print)

1089-7690 (online)

Publisher

$abstract.society.value is a Member of CrossRef

American Institute of Physics

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