Temperature-programmed desorption curves of m/z 27 of hydrogen cyanide HCN without exposure to the room-temperature atomic H-beam at 15 K (dotted line), and with exposure during 20 min (dashed line), one hour (dotted-dashed line) and three hours (full line). The warm atomic H₂ beam induces a change in morphology that shifts the desorption maximum to higher temperatures, as shown by the TPD curve obtained after three hours exposure to the H₂ beam with the plasma discharge off (large dashed line).