Can also use Pick
Pick[Alphabet[], Range[26], _?(EvenQ)]EvenQ]
Or for the more general case with spaces removed:
lst = "element of sel matches patt";
clst=DeleteCases[Characters[lst]," "];
Pick[clst,Range[Length[clst]],_?(EvenQ)]EvenQ]
{"l", "m", "n", "o", "s", "l", "a", "c", "e", "p", "t"}