Vapour-phase Raman spectra of chromium, molybdenum, and tungsten hexacarbonyls

Abstract

Vapour-phase Raman spectra of the hexacarbonyls [M(CO)6](M = Cr, MO, or W) have been recorded for the first time, and four of the six Raman-active fundamentals in the case of [Mo(CO)6] and [W(CO)6], and five of the six in the case of [Cr(CO)6]; have been located. The values obtained compare well with those obtained from analyses of the wavenumbers of combination bands in the infrared. The half-band widths of the ν1(a1g), ν2(a1g), ν3(eg), and ν11(t2g) fundamentals are 5–6, 9–13, 18–20, and 16–18 cm–1 respectively at the sample temperatures of 369 (Cr), 378 (MO), and 377 K(W). Rotational contours (OP. RS) to the non-totally symmetric bands are obscured by the presence of underlying hot bands. Vapour–solution wavenumber shifts are positive for the ν1(a1g) and ν3(eg) bands (both of which are CO-stretching modes), but negative for the ν2(a1g) and ν11(t2g) bands (MC-stretching and CMC-bending modes respectively). The relative values of the CO bond-polarisability derivatives, α⊥′/α∥′, from vapour-phase measurements, lie in the –0.265 to –0.24 region.