On the hexamethyldisiloxane dissociation paths in a remote Ar-fed expanding thermal plasma

In this paper we present primary hexamethyldisiloxane (HMDSO) molecule dissociation paths in a remote argon-fed expanding thermal plasma, where the HMDSO dissociation is initiated by charge exchange reactions with argon ions followed by dissociative recombination reactions with electrons. Investigation of the argon/HMDSO plasma chemistry by means of cavity ring down spectroscopy and threshold ionization mass spectrometry has allowed the detection and identification of radical species, such as CH x, SiCxHy and SiCHxO, and oligomerization products. The charge exchange reaction rate constant between argon ions and HMDSO molecules has been found to be equal to ( 4 +/- 2) x 10(-16) m(3) s(-1). This reaction has a dissociative character, i.e. the dissociation occurring at the Si - C and Si - O bonds accompanied by the abstraction of radicals, e. g. CH3 and OSi(CH3)(3). Under the experimental conditions investigated, the ions produced via charge exchange reactions lead to negligible ion-induced oligomerization routes. Instead, they undergo recombination reactions with electrons, leading to Si - O bond dissociation and further abstraction of methyl radicals.