Here is my translation of the Benedicamus hymn for Ascension: "Quando Christus ascenderat," as corrected by M. Herman Bonnus and included in Lossius "Psalmodia." While still a hymn of the Ascension, it links the Ascension and Session to Pentecost more explicitly than other hymns that focus on the Ascension itself. The text is based on the late medieval pia cantio of the same name, and uses the same melody. Here is the Pia Cantiones version of the melody.
The last line in the original is sung thus (note the length of 4th note):
WHEN Christ ascended into heav'n,
1. Quando Christus ascenderat,