sum of list elements of specific index of list : I want to find the sum of elements of the list of index 2, index3 and index3,index4 and index4,index5 on so on

like:- list=[7,5,9,4,7,11]  
 aspSum=[12,14,13,11,18]    ##  7+5, 5+9, 9+4, 4+7, 7+11


 please help me. I am new user of stackOverFlow, 