def format_rxn_header(reaction_id):
    """Returns string containing four-line RXN header."""
    #               <-A6-><---A9--><---A12----><--I7->
    #               IIIIIIPPPPPPPPPMMDDYYYYHHmmRRRRRRR
    return '$RXN\n\n      INFOCHEM             {:<7}\n'.format(reaction_id)