た
Auxiliary verb, See だ・2, だ after certain verb forms; indicate past or completed action
1. did, (have) done
See だ・3, indicates mild imperative
2. (please) do
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。