Parsing a txt file into data frame, filling columns based on the multiple separators

Question

Having a .txt file

structure as below

#n  1
a 1:0.0002 3:0.0003...
#n  2
b 2:0.0002 3:0.0003...
#n  3
a 1:0.0002 2:0.0003... 

trying t