The vibration-rotation emission spectrum of hot BeF2

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 nu3 fundamental band, the nu1+nu2, nu1+nu3, and 2nu2+nu3 combination bands, and 18 hot bands were assigned. The symmetric stretching (nu1), bending (nu2), and antisymmetric stretching (nu3) 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 nu3, nu1+nu3, and nu1+nu2 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 (Be) was determined to be 0.235 354(41) cm-1, and the associated equilibrium bond distance (re) is 1.3730(1) A. The results of our ab initio calculations are in remarkably good agreement with those of our experiment, and the calculated value was 1.374 A for the equilibrium bond distance (re). As in the isoelectronic CO2 molecule, the Fermi resonance in BeF2 is very strong, and the interaction constant k122 was found to be 90.20(4) cm-1.

Rotational ℓ-type resonance in BeH2, BeD2, and MgH2

“…CO 2 , CS 2 , and BeF 2 are good examples of symmetric linear triatomic molecules for which experimental data are available for the 02 2 0͑⌬ g ͒ and 02 0 0͑⌺ g + ͒ states. [6][7][8] There is no ambiguity in the assignments for these molecules because to 152.3.102.242. Redistribution subject to AIP license or copyright; see http://jcp.aip.org/about/rights_and_permissions their 02 0 0͑⌺ g + ͒ states are in strong Fermi resonance with the nearby 10 0 0͑⌺ g + ͒ states, and thus lie much lower in energy compared with the 02 2 0͑⌬ g ͒ states.…”

Combined gas electron diffraction/mass spectrometric study of beryllium diiodide assisted by quantum chemical calculations: structure and thermodynamics of beryllium dihalides

“…Comparison of the most precise to date experimental value of equilibrium r e (Be-F) = 1.3729710(95) Ǻ distance [24,25] with predictions of high-level QC calculation demonstrates slightly (within 0.01 Ǻ ) overestimated theoretical results. In the more recent FT IR study of BeF 2 , Yu et al [25] found the equilibrium distance 1.3730(1) Ǻ with one order larger error limit stated as that in earlier work [24,25]. In the early GED study of Akishin et al [4] published in 1958, though within large uncertainties of GED result typical for those days, the results are acceptably comparable with the contemporary GED data, except the case of BeI 2 .…”

“…The MP2 method systematically underestimates this frequency. From the high-resolution infrared emission spectrum of hot, 1273 K, BeF 2 , Yu et al [25] determined the vibration frequencies for BeF 2 , m 1 = 769.0943(2), m 2 = 342.6145(3) and m 3 = 1555.0480(1) cm -1 , with unexpectedly low error limit declared. This work provides the first experimentally determined value of m 1 , and it is noticeably the larger ''harmonic'' theoretical values (Table 4).…”

“…Results obtained by using an approximation by Bartell [26] suppose that the difference r g -r e is mostly caused by anharmonicity of valence vibrations: r e ¼ r g À 3 2 a 3 l BeÀX ð Þ 2 . The anharmonicity constants a 3 were accepted to be equal to 1.7 (BeF 2 ) and e Equilibrium r e values estimated from the experimental GED data by approximation by Bartell [26] as r e = r g -3/2(a 3 l 2 ) f Found from analysis of Fourier transform IR emission spectra: by Frum et al [24] (upper line) and Yu et al [25] (lower line) g Data of Akishin et al [4]; temperature of the experiment was not indicated in the original paper a Theoretical amplitudes were estimated on the base of the force field taken from the results of quantum chemical calculations by using the programs ANACOR [22] (CCSD(T)) and SHRINK [28] (B3LYP, MP2) 1.5 Å -3 (BeCl 2 , BeBr 2 and BeI 2 ) as estimated at diatomic approximation on the base of mean bond energies in BeX 2 molecules (637, 462, 398, 299 kJ/mol) [7] and symmetric valence vibration force constant F 1 (5.8, 3.3, 2.7 and 2.2 mdyn/Å for BeF 2 , BeCl 2 , BeBr 2 and BeI 2 , respectively). The latter were estimated from the vibration frequencies ( Table 4).…”

“…The high-level quantum chemical calculations, CCSD(T)/cc-pVBZ (B = T, Q, 5), performed for BeF 2 [25] derived the values of the Be-F distance ranging from 1.382 to 1.379 Ǻ in the series B = T to 5, and the equilibrium bond distance length was estimated to be 1.374 Ǻ by adding the corrections for the core-electron correlation effects to value obtained with the valence basis set of quintuple-zeta quality. (13) x (I 2 ) 5.1 (7) [0] 7.7(7) Effective and equilibrium structures For all halides the applied theoretical approaches DFT-B3LYP, MP2 and CCSD(T) yielded in satisfactory results as compared with the effective r g (Be-X) bond lengths determined from GED, within 0.01 Ǻ .…”