Does an oath of divorce for not smoking take effect if one accidentally inhales, knowing that the intention was only not to smoke cigarettes?

If your oath was to directly abstain from smoking, then you do not break your oath by the smoke reaching your stomach due to sitting near smokers.

However, you must quit smoking and avoid sitting with smokers for two reasons: 1. Not sitting with them is more conducive to not returning to smoking. 2. Islamic law prohibits sitting with disobedient people when they are directly committing a sin, as Allah the Almighty says: "And He has already revealed to you in the Book that when you hear the verses of Allah being denied and ridiculed, do not sit with them until they enter into another conversation. Indeed, if you did, you would be like them." (An-Nisa: 140).

So, if you sit in a gathering where there is a smoker, gently admonish him. If he insists, then leave the gathering.