Howard H. Claassen

Raman Spectra of MoF6, TcF6, ReF6, UF6, SF6, SeF6, and TeF6 in the Vapor State

Raman spectra of MoF6, TcF6, ReF6, UF6, SF6, SeF6, and TeF6 have been observed for the gaseous state using laser excitation. Some assignments of fundamental frequencies have had to be revised from previously accepted values. The overtone 2ν6 was observed for all these gaseous hexafluorides and several other overtones were observed for some of the molecules. Considerable broadening of the eg and f2g fundamentals was observed for TcF6 and for ReF6. This broadening is attributed to dynamic Jahn–Teller coupling. The best currently available measured values of fundamental frequencies for all 15 hexafluoride molecules of known Oh symmetry are tabulated.

Molecular force fields of octahedral XF6 molecules

Abstract The orbital valency force field (OVFF) is applied to the fifteen hexafluorides whose vibrational frequencies are known, and the best-fit force constants are calculated. The OVFF showed definite advantages over the more widely used UBFF model in that (a) the angular coordinates contain no redundancy; (b) the agreement with the observed frequencies in the angle deformation modes is far superior; and (c) the least squares calculation procedure yields rapidly-converging sets of force constants for all fifteen hexafluorides. The f 1 u force constants of some of the hexafluorides are determined from their infrared band envelopes and are compared with the calculated values. The angle distortion constant D and the repulsion constant F are found to have strong dependence upon the number of nonbonding electrons in the 4 d and 5 d transition metal series. This effect is discussed in terms of the repulsion between the nonbonding and bonding electrons and the Coulombic forces between partially ionic fluorine atoms.

Force Constants of Metal Hexafluorides

Equations are given relating fundamental frequencies and force constants for a general quadratic potential function for XY6 molecules of symmetry Oh. Tables of force constants are given for hexafluorides of Mo, W, Re, Os, Ir, Pt, U, Np, and Pu.

Vibrational Spectra of IOF5, OsOF5, and ReOF5

Raman spectra of IOF5, OsOF5, and ReOF5, and the infrared spectra of OsOF5 and ReOF5 are presented, all for the gaseous state. Complete assignments of fundamental frequencies are made, and these confirm the expected C4ν symmetry. Fundamental frequencies in cm−1 in the order, 4a1, 2b1, b2, and 4e, are: for IOF5, 927.0, 680.4, 640.2, 362.9, 647, 307, ∼  330, 710.3, 372.2, 343, and 204.8; for OsOF5, 962.6, 716.4, 644, 280.5, 644, 210, 332, 700.6, 263, 367, and 164; and for ReOF5, 989.8, 738.6, 643, 309, 652, 234, 334, 713.0, 260, 365, and 125 cm−1.

Infrared Spectra of VOF3 and POF3

The infrared spectrum of VOF3 has been studied and interpreted in terms of a C3v molecular symmetry. All six fundamentals have been observed: the a1 frequencies are 1057.8, 721.5, and 257.8 cm−1 and the e frequencies are 806, 308, and 204.3 cm−1. The infrared spectrum of POF3 has also been studied and the lowest e fundamental, earlier observed in the Raman spectrum, has been confirmed.

Vibrational Spectra of OsF6 and PtF6

Infrared absorption spectra of gaseous OsF6 and PtF6 from 6–50μ and the Raman spectrum of liquid OsF6 are reported. These are interpreted in terms of the octahedral point group Oh, and the six fundamental frequencies are determined. Their values and symmetry species are for OsF6 733 (a1g), 632 (eg), 720 (f1u), 268 (f1u), 252 (f2g), and 230 (f2u); for PtF6 655 (a1g), 601 (eg), 705 (f1u), 273 (f1u), 242 (f2g), and 211 (f2u). Thermodynamic functions, including electronic contributions, are calculated for the ideal gaseous state of both compounds.A comparison of the details of the vibrational spectra of eleven hexafluorides reveals certain characteristic features for OsF6 and ReF6. Since only these two molecules have appropriately degenerate electronic ground states these differences are interpreted as evidence of a Jahn‐Teller effect.

Raman Spectra for XeF2, XeF4, and XeOF4 Vapors, and Force Constant Calculations

Raman spectra of the vapor phase have been observed for XeF2, XeF4, and XeOF4. These, together with published infrared spectra, provide vapor values for all but one of the 19 vibrational frequencies of these three molecules. Normal coordinates and force constants are determined in terms of the orbital valency force field model, including repulsions between lone‐pair electrons and fluorine atoms.

Spectral Observations on Molecular XeF6: Raman Scattering and Infrared, Visible and Ultraviolet Absorption in the Vapor and in Matrix Isolation

Raman spectra and visible and ultraviolet absorption spectra of XeF6 vapor have been studied as functions of temperature. The changes that occur in the observed spectra are interpreted as due to relative population changes of the three electronic isomers postulated in the preceding paper. Evidence is presented that, even at temperatures as high as 100°C, it may take tens of minutes to reach equilibrium among the isomers. Infrared spectra of both XeF6 vapor at 25°C and of XeF6 molecules isolated in a low temperature argon matrix have been studied for a variety of previous thermal treatments of the XeF6 samples. In the spectra of the matrix, large differences in the relative intensities of absorption bands were found, depending on the thermal history of the XeF6 used in the deposition. All the spectra observed are interpreted in terms of the three electronic isomers, and the assignments appear quite plausible.

Vibrational Spectra and Thermodynamic Properties of ClF3 and BrF3

The Raman and infrared spectra of ClF3 and BrF3 have been studied. The spectra of ClF3 give strong support for a planar T‐shaped molecular model. The spectra of BrF3 are less complete but are sufficiently similar to that of ClF3 to confirm a like shape for this molecule. The fundamental vibrational frequencies of ClF3 observed for the vapor are 326(a1), 364(b2), 434(b1), 528(a1), 703(b1), and 752(a1) cm‐1. S0 for ClF3, calculated statistically at the boiling point, 11.75°C, is 66.60 cal mole‐1 deg‐1 compared to the value of 67.04 obtained from a revised calculation of this quantity from available thermal data. For BrF3 only two fundamental frequencies were observed in the vapor, 613(b1) and 674(a1) cm‐1; the others were estimated by a normal coordinate calculation. S0 for BrF3 calculated statistically is 70.86 cal mole‐1 deg‐1 at 43.11°C compared to a value of 71.90 calculated from available thermal data. Tables of the thermodynamic functions of ClF3 and BrF3 from 250 to 1000°K are given.

Infrared and Raman Spectra of Krypton Difluoride

The infrared and Raman spectra of KrF2 vapor have been obtained. They clearly indicate a linear and symmetric molecule with the symmetric stretching frequency at 449 cm−1, the asymmetric stretching frequency at 588 cm−1, and the bending frequency at 232.6 cm−1. The force constants are fr=2.46, frr=−0.20, and fα=0.21 mdyn/A. The negative bond—bond interaction constant can be explained neither by valence bond models nor by a simple molecular orbital model.