途端, とたん
Adverb
just (now, at the moment, etc.), just as, in the act of, as soon as, at the moment that
これをきいたとたん、彼は真っ青になった。
に
Particle
1. at (place, time), in, on, during
2. to (direction, state), toward, into
3. for (purpose)
4. because of (reason), with
5. by, from