VICTOR J. HERRERO, R. ESCRIBANO, B. MATÉ, O. GÁLVEZ, I. K. ORTEGA, B. MARTIN-LLORENTE, Instituto de Estructura de la Materia, CSIC, Madrid, Spain; P. J. GUTIÉRREZ, Instituto de Astrofísica de Andalucía, CSIC, P.O.Box 3004, 18080 Granada, Spain.
Frozen CO2 is, after water, one of the main components of cometary nuclei. The structure of CO2 ice in interaction with water ice depends on several factors, like deposition scheme, temperature or density. We present an investigation on ice mixtures of water and CO2 and their variation with temperature, based on temperature programmed desorption (TPD) and infrared spectroscopy measurements. Two slightly different CO2 structures are shown to exist, and their relative concentration is found to depend critically on the deposition sequence and temperature of the sample.