the moment that; just as

たとたんに means that the instant one thing happened, something else (often unexpected) immediately followed. Attach it to a verb's past form. The second clause describes a spontaneous, often surprising result, not a planned action.

Examples

• 家いえを出でたとたんに、雨あめが降ふり出だした。

  Ie o deta totan ni, ame ga furidashita.

  The moment I left the house, it started to rain.

• ベッドに入はいったとたん、眠ねむってしまった。

  Beddo ni haitta totan, nemutte shimatta.

  The instant I got into bed, I fell asleep.

Vocabulary in these examples

• 家 house; home
• 出る to leave; to exit
• 雨 rain
• 降る to fall (rain, snow)
• 出す to take out; to submit
• ベッド bed

Related patterns · Time and sequence

• 〜際に on the occasion of; when
• 〜に先立って prior to; in advance of
• 〜て以来 ever since
• 〜次第 as soon as
• 〜最中に in the middle of; right while