def index_map(idx_lines):
    """Returns a map from the orbital index to its descriptive quantum
    numbers
    :param idx_lines: lines defining the index -> orbital key
    """
    idx_map = dict()
    for line in idx_lines:
        row = line.split()
        row[0] = int(row[0])
        idx_map[row[0]] = tuple(row[1:])
    return idx_map