Gas phase ionisation of carbon disulfide clusters at terawatt laser intensity: Generation of singly and multiply charged atomic and molecular ions

Gas phase ionisation of carbon disulphide clusters (CS2)(n) with different laser wavelengths of terawatt intensity has been studied using time-of-flight mass spectrometry. In the mass spectra, series of singly charged cluster fragments such as C+, S+, CS+, [C(Cs)](+), [S(CS)](+), [S-2(Cs)](+), [C(CS2)](+), [C-2(CS2)](+), [C-3(CS2)](+), [S(CS2)](+), S-2(+),S-3(+),[CS(CS2)](+) etc. were observed at 266 nm photoionisation. Higher cluster fragments formation has been rationalised based on various ion-molecule reactions that occur within the cluster following ionisation. One of the prominent cluster fragment was S-2(+) whose formation mechanism has been explained based on two competitive ion-molecule reactions. Photoionisation at 355 nm leads to formation of doubly charged carbon and iodine ion along with singly charged cluster fragments. An increase in charge state of carbon and sulphur ions (up to + 4 state) was observed on changing the laser wavelength to 532nm, indicating efficient interaction of CS2 clusters at longer wavelength. In order to elucidate the mechanism of formation of multiply charged atomic ions at 355 and 532 nm, energy of electrons released on ionisation of CS2 cluster at different wavelengths was measured. Based on these experimental results, energisation of electrons within the cluster was observed due to influence of electric field of the laser pulse. The extent of energisation was found to be more at longer wavelength indicating role of electron impact ionisation for generation of multiply charged ions at this laser intensity conditions. Apart from multiply charged atomic ions, doubly charged molecular ion (CS22+) was also observed at 532 nm. Generation of CS22+ is explained based on similar ionisation mechanism as described for atomic multiply charged ions. However, lifetime of the doubly charged ion plays an important role for generation of the ions under our experimental conditions.