That would be a little bit embarrassing. I found the answer, too. And according to the reference, inorganic chemistry, NaCl in gas phase would like molecule.
Does it mean that the ionic bond to hold Na+and Cl- to form compound stronger than the similiar bond to form crystal?
Or some something else happen some bond break and some dose not?
Accurate Equilibrium Structures Obtained from Gas-Phase Electron Diffraction Data: Sodium Chloride
Philip D. McCaffrey ,† Richard J. Mawhorter ,‡ Andrew R. Turner ,† Paul T. Brain ,† and David W. H. Rankin *†
School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, United Kingdom, and Department of Physics and Astronomy, Pomona College, 610 North College Avenue, Claremont, California 91711-6359