This is traditional Marian antiphon of Eastertide and can take the place of the Angelus during the Easter season.
Find the notation here: https://gregobase.selapa.net/chant.php?id=2290
The traditional antiphon chanted before the Invitatory Psalm.
Chant Notation: https://gregobase.selapa.net/chant.php?id=7290
Full Liber Hymnarius PDF can be downloaded here (antiphon on page 79): https://www.gregorianum.org/wiki/Liber_Hymnarius_1983_(Antiphonale_Romanum_Tomus_Alter)