Attack: Intelligence vs. Fortitude
Hit: "1d6 + Intelligence modifier cold damage, and the target is slowed until the end of your next turn.
"Level 21: 2d6 + Intelligence modifier cold damage."[PH:159][Dr401:53]
Ray of frost is an at-will power available to wizards at 1st level.
The "Class Compendium: The Arcanist" article in Dragon 401 added the evocation keyword to ray of frost.