A Line Mechanic removed and replaced a crew oxygen bottle on a B737-300 aircraft at the gate. While completing the paperwork he realized the part effectivity for the bottle he installed did not match the aircraft model number. Aircraft had already departed.

Narrative

I received a gate call; understanding that the crew oxygen bottle was low. Understanding that I did not have enough time to service it I grabbed a bottle from the Stock Room and proceeded to the aircraft to the R/R (Remove and Replaced) bottle. Completed task and signed-off aircraft logbook and headed back to the office. Upon completely filling out Form X and looking over all paperwork I then realized the Part Effectivity did not match my aircraft model number. [I] immediately notified Lead Mechanic and called Operations to stop aircraft from leaving gate...but it was too late as aircraft was gone. I did not think to check our Maintenance/Parts effectivity computer system as I did not know/think that the oxygen bottles were any different other than size and material.I had worked a 24-hour shift the day prior...but felt physically and mentally good at the time the event occurred. I do not normally work this shift and routinely service oxygen bottles on my normal shift. Ultimately my thoughts of 'limited time stress' and oversight of looking up Parts Effectivity and overlooking correct procedures caused my situation.