  We propose, on the basis of our first principles density functional based
calculations, a new isomer of graphane, in which the C-H bonds of a hexagon
alternate in 3-up, 3-down fashion on either side of the sheet. This 2D puckered
structure called 'stirrup' has got a comparable stability with the previously
discovered chair and boat conformers of graphane. The physico-chemical
properties of this third conformer are found to be similar to the other two
conformers of graphane with an insulating direct band gap of 3.1 eV at the
{\Gamma} point. Any other alternative hydrogenation of the graphene sheet
disrupts its symmetric puckered geometry and turns out to be energetically less
favorable.
