Field emission microscopy (FEM) observations of behaviors of a single nitrogen molecule on a pentagon at the tip of a multiwall carbon nanotube and an attempt to control a desorption of the nitrogen molecule by pulse laser irradiation were carried out. The adsorbed gas molecule was recognized as a bright spot in a FEM image. In an adsorption of nitrogen, two types of bright spot were observed. They reflected two types of adsorption state that a molecular axis of the nitrogen was parallel or perpendicular to substrate pentagon. At energy density of under 35 mJ/cm(2) the pulse laser irradiation was a responsive method to promote a desorption of physisorbed molecule without any damage to substrate pentagon. (c) 2007 American Vacuum Society.