Explanation
Express the moment something happens; 'as soon as', 'the moment', 'the instant'.
Formation
Verb-た form + とたん
Detailed explanation
The ～たとたん grammar point is used to express that something occurs immediately at the exact moment another action is completed. It can be translated as 'as soon as', 'the moment', or 'the instant' in English. It is attached to the past tense (た-form) of a verb.
Examples
Doa wo aketa totan, neko ga nigedashita.
As soon as I opened the door, the cat ran away.
Denwa wo kaketa totan, denchi ga kireta.
The moment I made the phone call, the battery died.
Ame ga furihajimeta totan, minna ga kasa wo sashita.
The instant it started raining, everyone put up their umbrellas.
Kare ni atta totan, kare no egao ga kieta.
As soon as he met me, his smile disappeared.
Practice
Grammar content sourced from hanabira.org.