Collision-induced alignment of H₂O⁺ drifting in helium

The collision-induced alignment of H2 O+ drifting in helium is studied with a molecular dynamics method that has been extended to treat nonlinear rigid ions. Rotational distribution functions and averaged quantities are presented in terms of the ρ formalism [M. Thachuk, Phys. Rev. A 72, 032722 (2005)], and it is shown that this description gives a very good agreement with simulation results. In addition to velocity and angular velocity autocorrelation functions, a velocity-angular velocity cross correlation function is introduced. This cross correlation function provides insight into the dynamical nature of the alignment mechanism.