Asymmetry of Photoelectron Angular Distributions in Molecules by Intense Attosecond Extreme Ultraviolet Laser Pulses

We present photoelectron angular distribution of the aligned molecular ion H₂⁺ by intense ultrashort attosecond extreme ultraviolet laser pulses from numerical solutions of timedependent Schr?dinger equations. Photoionization from a superposition state of the ground 1sσ_g and the excited 2pσ_u states with pulses at photon energies above the ionization potential, ?ω>Ip, and intensity 10¹⁴ W/cm², yields pulse duration dependent asymmetry of photoelectron angular distributions. We attribute the asymmetry to the periodical oscillation of the coherent electron wave packets, resulting from the interference of the two electronic states. For the processes with long pulse durations, such duration dependence is absent and symmetric angular distributions are obtained.