Calculations are performed for H 2 at 0.75 Å separation in a spin-unrestricted formalism, with the field aligned along the internuclear axis; we take this to be polarization in the z direction, n F = (0, 0, 1). The external field mimics a laser field with intensity of I = 10 14 W/cm 2 and carrier frequency ω 0 = 1.55 eV (= 800 nm). In atomic units, this corresponds to A = 0.05 a.u. and ω 0 = 0.057 a.u. in Eq. (19). For the Gaussian-impulse field [Eq. ( )], we take t c = 800 a.u. and σ = 200 a.u., and use a total simulation time of 1500 a.u. (≈ 36.3 fs), extending just beyond the support of the envelope function E(t) for this set of parameters. We also report simulations using a continuous-wave field where the total simulation time is 5,000 a.u. (≈ 121 fs). These simulations use the same values A and ω 0 that define the the impulsive field, so that the peak value of E(t) is the same in both cases. (Both fields are plotted in Fig. .) At low field intensities, vibrational motion may destroy coherences needed to obtain the highest harmonic orders 66 but is not considered here, where we use an ionizing field intensity.