def r_local(denis, alt):
    """Local recombination from Sultan eq 21 alpha*n_mol
       Risbeth & Garriott '69: Dissociative recombination is the principal
       E and F region loss mechansim.
       Huba '96: RTI not damped by recombination in F region
       n_mol is the concentration of molecular ions
       alpha = 2*10**(-7) according to Sultan '92
       alpha ~ 10**(-7) according to Risbeth & Garriott '69
    """
    n_mol = 0
    if alt < 200:
        return 0
    for i, n_i in enumerate(denis):
        if i == 2 | i == 3 | i == 5:
            n_mol += n_i
        
    return n_mol*2*10**(-7)