The Flash : Really liked the music theme in Iris' death scene…

It was sad and haunting at the same time. Accentuated the scene quite well.

I agree! As beautiful as it is tragic. It's Barry's and Iris's theme song! The tune is similar to the songs that play during Barry's and iris's kiss scenes and it's the same song played during the kiss they shared last season on the porch steps. A lovely tune for a lovely couple.
Update:
A variation of the song is also played during their porch scene in 3x02 as well as during their scene in the speed force together in season 2.

James 4:8
Easier to say you're right than I'm wrong.