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We address the collision of two superfluid 4 He droplets at non-zero initialrelative velocities and impact parameters within the framework of liquid 4 Hetime-dependent density functional theory at zero temperature. In spite of thesmall size of these droplets (1000 He atoms in the merged droplet) imposed bycomputational limitations, we have found that quantized vortices may be readilynucleated for reasonable collision parameters. At variance with head-oncollisions, where only vortex rings are produced, collisions with non-zeroimpact parameter produce linear vortices which are nucleated at indentationsappearing on the surface of the deformed merged droplet. Whereas for equal-sizedroplets vortices are produced in pairs, an odd number of vortices can appearwhen the colliding droplet sizes are different. In all cases vortices coexistwith surface capillary waves. The possibility for collisions to be at theorigin of vortex nucleation in experiments involving very large droplets isdiscussed. An additional surprising result is the observation of the dropscoalescence even for grazing and distal collisions at relative velocities ashigh as 80 m/s and 40 m/s, respectively, induced by the long-range Van derWaals attraction between the droplets.

Quantized vortex nucleation in collisions of superfluid nanoscopic helium droplets at zero temperature