def activation_energy(molecule):
    """
    Extracts the final energy of a reactant from an Orca output file.

    **Parameters**

        molecule: *str*
            A string for the name of the simulation containing
            the optimized reactant.

    **Returns**

        E_tmp: *float*
            The energy of the optimized reactant.
    """
    lines = []
    E_tmp = 0
    f = open('orca/%s/%s.out' % (molecule, molecule), 'r')
    for line in f:
        lines.append(line.strip().split())
    f.close()
    for j in range(len(lines)):
        if len(lines[j]) > 4:
            if lines[j][0] == 'FINAL' and lines[j][1] == 'SINGLE' and lines[j][
                2] == 'POINT' and lines[j][3] == 'ENERGY':
                E_tmp = float(lines[j][4])
                break
    return E_tmp
