Knowledge Bank

A new method of making ice samples with large surface areas by depositing nanocrystals of ice on an IR transparent window, has increased the intensity of surface-defect modes, and has greatly improved signal to noise levels. This allows a comprehensive look at the IR adsorption of surface molecules by climinating bulk-ice bands. Difference spectra are used to eliminate overlapping bulk-ice bands in the following ways; difference spectra between a) two spectra of the same sample at the same temperature with the only difference being the amount of annealing of each spectrum and b) bare surface spectra and adsorbate saturated surface spectra at the same temperature, showing adsorbate-shift of surface-defect modes. A useful simulated difference spectrum is available, generated by V. Buch using a highly annealed amorphous ice cluster for the surface and cubic ice for the $interior.1$ Comprisons between experimental and simulated spectra have yielded the assignment of the antisymmetric surface-defect modes of the dangling-D $(-2725cm-1)$ dangling-O $(\sim 2645cm-1)$, and the surface 4-coordinate $D2O$ molecules $(\sim 2580cm-1$).