Chemisorption vs Physisorption?
It appears to be one of degrees of bonding, without a clear distinction. As stated in this Wikipedia article:  


  Physisorption, also called physical adsorption, is a process in which
  the electronic structure of the atom or molecule is barely perturbed
  upon adsorption.$\mathrm{^{[1][2][3]}}$


A more thorough description is given later in the article:  


  "The fundamental interacting force of physisorption is caused by van
  der Waals force.   [...]   In comparison with chemisorption, in which
  the electronic structure of bonding atoms or molecules is changed and
  covalent or ionic bonds form, physisorption, generally speaking, can
  only be observed in the environment of low temperature (thermal energy
  at room temperature ~26 meV) and the absence of the relatively strong
  chemisorptions. In practice, the categorisation of a particular
  adsorption as physisorption or chemisorption depends principally on
  the binding energy of the adsorbate to the substrate."


1) K. Oura; et al. (2003), Surface Science, An Introduction, Berlin: Springer, ISBN 978-3-540-00545-2
2) M. C. Desjonqueres; et al. (1996. Corrected printing 1998), Concepts in surface physics (2nd ed.), New York: Springer-Verlag, ISBN 3-540-58622-9
3) Hans Luth; et al. (1993), Surfaces and interfaces of solids, Springer-Verlag, ISBN 978-3-540-56840-7