Yes, the "in persona Christi" is the sacerdotal role and no, it is not part of the diaconate.

You seem to be confusing "sacerdotal" with "ordained".

CCC 1538 Integration into one of these bodies in the Church was accomplished by a rite called ordinatio, a religious and liturgical act which was a consecration, a blessing or a sacrament. Today the word "ordination" is reserved for the sacramental act which integrates a man into the order of bishops, presbyters, or deacons, and goes beyond a simple election, designation, delegation, or institution by the community, for it confers a gift of the Holy Spirit that permits the exercise of a "sacred power" (sacra potestas) which can come only from Christ himself through his Church. Ordination is also called consecratio, for it is a setting apart and an investiture by Christ himself for his Church. The laying on of hands by the bishop, with the consecratory prayer, constitutes the visible sign of this ordination.