Wavelength dependent photoionisation of ethanol clusters: generation of hydrogen like C5+ ions at terawatt laser intensity

Abstract

Photoionisation of ethanol clusters has been investigated at different laser wavelengths over the intensity range of ∼10¹²–10¹³ W cm⁻². Under 266 nm ionisation, singly charged fragments and protonated cluster ions (up to (C₂H₅OH)₉H⁺) were observed in the mass spectrum. Moreover, small ion signals corresponding to doubly charged carbon ions (C²⁺) were also observed. At longer laser wavelengths (i.e. 355, 532 and 1064 nm), the charge states of multiply charged ions of C and O were found to increase systematically and the maximum observed charge states were C⁵⁺ and O⁶⁺ at 1064 nm. Generation of C⁵⁺ ions (IE: 392 eV) is noteworthy as it requires removal of a core shell electron from a carbon atom. A comprehensive study has been carried out to appreciate the ionisation mechanism of such higher charge state formation in an ethanol cluster at terawatt laser intensity. A laser power dependency study suggests the role of multiphoton ionsation in creating initial charge centres within the cluster. Subsequently the ionised electrons produced upon multiphoton ionisation gain energy from the laser field and cause further ionisation via electron impact ionisation. Energisation of electrons and generation of multiply charged atomic ions were found to depend on the stability of clusters in the laser field which in turn is related to intermolecular interactions of ethanol clusters. Moreover, anionic fragment ions were observed in the ionisation of ethanol clusters at ∼10¹² W cm⁻² which also influences the ionisation dynamics of the cluster.