The CO:CO2 complex in argon matrices: Experimental evidence for two conformations with spontaneous interconversion

• Published in: The Journal of chemical physics 1995-06, Vol.102 (23), p.9235-9239
• Main Authors: Raducu, V., Jasmin, D., Dahoo, R., Brosset, P., Gauthier-Roy, B., Abouaf-Marguin, L.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.468873

The CO:CO2 complex in argon matrices is identified near the CO absorption which appears at 2138.49 cm−1, slightly shifted from the pure argon value of 2138.64 cm−1, because of the presence of CO2. It exhibits two features on each side of the CO frequency: a doublet at 2143.34 and 2143.01 cm−1 (HF A and B lines) and a narrow line at 2135.38 cm−1 (LF line); these small shifts indicate weakly complexed C–O stretching modes. When the temperature is raised from 5 to 12 K, the LF line decreases progressively and disappears at the benefit of the HF A and B lines, the total absorption intensity remaining unchanged. This effect is perfectly reversible and can be explained by an exchange between two different conformations of the CO:CO2 complex, with complexed C–O bonding shifted either towards a higher frequency (HF form), or towards a lower one (LF form). Furthermore, after a fast cooling down to any given temperature below 12 K, the intensity ratio between the two forms is time dependent; the high temperature form (HF form) converts into the LF form within a few minutes. The equilibrium value of the intensity ratio LF/HF and the rate constants for the conversion are temperature dependent. We have checked that this conversion, occurring without any temperature change, is not photoinduced.