Bb Minor Add9, 1st inversion (C# in the bass)
Also written as Bbmadd9/C#.
Notes, from the bass up
C# (bass)E#B#A#
The same notes as Bb Minor Add9 (C#, E#, B# and A#), rearranged so C# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.