Very low H-O-H bending frequencies. vi. vibrational spectra of CdCl₂·H₂O

The infrared and Raman spectra of CdCl2·H₂O as well as those of a series of its partially deuterated analogues were recorded at room and at liquid-nitrogen temperature (RT and LNT, respectively). The combined results from the analysis of the spectra were used to assign the observed bands. In the difference IR spectrum of the compound with low deuterium content (≈ 4 % D) recorded at RT, one broad bands is observed at around 2590 cm^-1 while in the LNT spectrum two bands appear (at 2584 cm –1 and 2575 cm ^-1 ). The appearance in the LNT spectrum of these two bands which are due to the stretching OD modes of the isotopically isolated HDO molecules points to the existence of two crystallographically different hydrogen bonds and is in accordance with the structural data for this compound. In the LNT infrared and Raman spectra of the protiated compound , one band, at 1583 cm^-1 , is observed in the region of the bending HOH vibrations with a frequency that is decreasing with lowering the temperature. An interesting finding related to this band is that its frequency is lower than that for the water molecule in the gas phase ( 1594 cm ^-1 ). In the RT and LNT IR spectra, only one strong band (at 560 cm ^-1 ) is observed in the region of the liberations of water molecules (700 cm ^-1 – 400 cm ^-1 ). (author)