## Abstract

The high-resolution infrared emission spectrum of BeF2 vapor at 1000 degrees C was rotationally analyzed with the assistance of large-scale ab initio calculations using the coupled-cluster method including single and double excitations and perturbative inclusion of triple excitations, in conjunction with correlation-consistent basis sets up to quintuple-zeta quality. The nu(3) fundamental band, the nu(1)+nu(2), nu(1)+nu(3), and 2 nu(2)+nu(3) combination bands, and 18 hot bands were assigned. The symmetric stretching (nu(1)), bending (nu(2)), and antisymmetric stretching (nu(3)) mode frequencies were determined to be 769.0943(2), 342.6145(3), and 1555.0480(1) cm(-1), respectively, from the band origins of the nu(3), nu(1)+nu(3), and nu(1)+nu(2) bands. The observed vibrational term values and B rotational constants were fitted simultaneously to an effective Hamiltonian model with Fermi resonance taken into account, and deperturbed equilibrium vibrational and rotational constants were obtained for BeF2. The equilibrium rotational constant (B-e) was determined to be 0.235 354(41) cm(-1), and the associated equilibrium bond distance (r(e)) is 1.3730(1) angstrom. The results of our ab initio calculations are in remarkably good agreement with those of our experiment, and the calculated value was 1.374 angstrom for the equilibrium bond distance (r(e)). As in the isoelectronic CO2 molecule, the Fermi resonance in BeF2 is very strong, and the interaction constant k(122) was found to be 90.20(4) cm(-1). (c) 2005 American Institute of Physics.

Original language | English |
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Pages (from-to) | - |

Number of pages | 8 |

Journal | Journal of Chemical Physics |

Volume | 123 |

Issue number | 13 |

DOIs | |

Publication status | Published - 1 Oct 2005 |

## Keywords

- ALKALINE-EARTH DIHALIDES
- CORRELATED MOLECULAR CALCULATIONS
- GAUSSIAN-BASIS SETS
- METAL-HALIDES
- GAS-PHASE
- ELECTRON-DIFFRACTION
- INFRARED SPECTRA
- ION MODEL
- EQUILIBRIUM CONFIGURATION
- FORCE CONSTANTS