published as an Advance Article on the web 3rd August 2001 particles covering a vast size range from some nanometres up to some hundred nanometres were N 2 O (CO 2 ) formed by injecting gaseous into a collisional cooling cell at temperatures between 4 and 110 K. N 2 O (CO 2) FTIR spectroscopy was used to study the vibrational dynamics of the nanoparticles between about 600 and 4000 cm~1. For the spectra of the bigger particles formed at temperatures around 78 K, we have studied the inÑuence of the experimental conditions on the Ðne structure of the strong absorption bands and its temporal behavior. From an estimate of the particle sizes, we conclude that the observed changes in the Ðne structure are not simple size e †ects ; they are likely to be due to a change in the particle shape or in the molecular order. From a comparison with infrared spectra of clusters generated in a supersonic jet expansion, we estimate the size of the particles produced at temperatures below 10 K to lie around one nanometre.
Band structures in the region of strong infrared absorption bands for different N2O-12CO2 and 12CO2-13CO2 composite particles are investigated by combining quantum mechanical exciton calculations with systematic experimental investigations. The ice particles are generated by collisional cooling and characterized with rapid-scan infrared spectroscopy. The size of the particles lies between approximately 10 and 100 nm. The calculated spectra show excellent agreement with the experimental data. This work leads to a detailed understanding on a molecular level of shape effects in pure and statistically mixed particles as well as of the characteristic features observed for core-shell particles.
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