Temperature dependence of the absorption properties of silanol groups in amorphous SiO2: Are silanol groups organized in clusters?

► VUV and IR absorption of Si-OH groups in a- SiO2 are studied in the range T=(4-300)K. ► A process of conversion of free into H-bonded Si-OH groups is observed. ► Free Si-OH groups only are responsible of the VUV absorption. ► Si-OH groups are suggested being arranged in clusters in the a- SiO2 network.