Vibrational spectra of solid fluorine

Abstract

Raman and far infrared spectra of crystalline fluorine have been obtained in both solid phases. As expected for the disordered higher temperature form, only the Raman-active stretching fundamental is observed for β-F2. Near ∼ 20 °K α-F2 exhibits the following spectral features (in cm−1): Raman — ν(1 – 0) 985; ν(2 – 0) 1764; ν(libration) 44, 55, 77, (93?); infrared — ν(translation) 28, 42.5, 80. The predictions of a preliminary calculation of the optically active lattice frequencies for the low temperature phase are in poor agreement with the observed lattice frequencies, suggesting that an improved model will be required to help distinguish the correct α-F2 crystal structure. Solid fluorine more closely resembles oxygen that it does the other halogens. In particular, the intermolecular forces are extremely weak, as exemplified by the small shifts of the internal frequencies from their gas phase values, the absence of observable factor group splitting of the fundamental and the overtone, and the relatively low values of the external (lattice) frequencies.

Matrix Raman spectra of the molecular halogens: Resonance Raman spectra of isolated and aggregated I2

“…The observed F, fundamental in solid argon, 892 cm-' [19], is in agreement with the early gas-phase value [20] both of which are near the very recent solid phase measurement, 895 cm-' [21]. The observed F, fundamental in solid argon, 892 cm-' [19], is in agreement with the early gas-phase value [20] both of which are near the very recent solid phase measurement, 895 cm-' [21].…”

Elementary excitations in condensed oxygen (α,β,γ, liquid) by high-resolution Raman scattering

“…18 But then, in oxygen, one would expect a splitting of the vibron line ͑from vibrational overtone spectra we estimate ϳ0.2 cm Ϫ1 ) and two additional librons. The fact that the vibron splitting was not observed in fluorine whereas the additional librons have been observed 19 is caused by the resolution (1.5 cm Ϫ1 ) of the named measurement. Therefore high resolution Raman measurements (0.01 cm Ϫ1 ) are necessary to clarify the question if the structure of ␣-O 2 is C2/m or C2/c.…”

The Crystal Structures of α‐ and β‐F2 Revisited

“…15) to be correct,a st he refinement in space group C2/m gave very poor results (see SupportingI nformation). The refined lattice parameters are a = 5.4780(12), b = 3.2701 (7), c = 7.2651 (17) , b = 102.088(18)8, V = 127.26(5) 3 , mS8, Z = 4a t1 0K.T herefore, a-F 2 is not isotypic to a-O 2 . [6] The crystal structure of a-F 2 is shown in Figure2.T able 1h olds the atomic coordinates,W yckoff positions, site symmetries ando c- The crystal structure of a-F 2 (left, projection along a-axis).…”

“…In the experimental Raman spectrum measured with spectrals lit width of circa 0.5 cm À1 the low-intensity B g -mode could not be distinguished from the A g -mode. [17] Even thought he FÀFs tretching frequency calculatedo nt he DFT-PBE0 level of theory is clearlyo verestimated, the calculated Raman and IR spectra enablec omparisons of the lowenergy librational modes with the experimental spectra. [17] Four librational modes have been observed in the lattice vibration region of the a-F 2 Ramans pectrum:9 3, 77, 55, and 44 cm À1 .I nt he calculated spectrum, the corresponding values are 101, 71, 58, and 16 cm À1 .T he experimental IR spectrum showedl ibrationalm odes at 80, 42.5, and 28 cm À1 .T he corresponding DFT-PBE0 modes are 90, 41, and 32 cm À1 ,w ithl ow absorbances of 0.02, 0.03, and 0.01 km mol À1 .…”

“…The Ramanf requency of the FÀF stretching vibration in solid a-F 2 has been reported at 895 and 894 cm À1 in previouss tudies. [11,17] Here the FÀFs tretching frequencyp redicted with DFT-PBE0 is 1096 cm À1 .B ecause there are two F 2 molecules in the unit cell, there are in fact two FÀF stretching modes:A nA g -symmetric mode where the F 2 molecules are vibrating in the same phase, and a B g -symmetric mode where the F 2 molecules are vibrating in anti-phase. The frequency differenceb etween these two modes is less than 0.5 cm À1 and the intensity of the B g -modei so nly 8% of the A gmode.…”