A Comparative Study on Ionization-Induced Dissociation of Methane, Irradiated by 800 nm and 400 nm Laser Fields

Irradiation of methane by intense laser fields leads to the production of several molecular ions CH n m+ (m = 1, 2 with n = 0–4) and atomic fragments such as H n m+ (m = 0, 1 with n = 1, 2) as a result of dissociation [1]. Previous studies on methane ionization irradiated by pulses of nanosecond duration [2] showed an absence of the parent fragment CH 4 + in the time-of-flight (TOF) spectrum. This was explained as a result of the dissociation into the CH 3 + and a hydrogen atom. On the other hand, when the pulse duration was decreased down to 8 fs [3] all the fragment ions disappeared except for the CH 4 + and CH 3 + molecular ions indicating that methane did not have enough time to dissociate after the ionization step. All the aforementioned studies were confined to the fundamental wavelength of 800 nm. In the present work, we extend the study to include the second harmonic field at 400 nm.