Aq_excit_n_m Function

function Aq_excit_n_m(eb ,q, n, m) result(sigma)
    !+Calculates the excitation cross section for a neutral Hydrogen atom transitioning from
    !+the `n`\(\rightarrow\)`m` state due to a collision an ion with charge `q` at energy `eb`
    !+
    !+@note Uses specialized cross sections if available else uses generic cross sections
    !+
    !+###Equation
    !+$$ A^{q+} + H(n) \rightarrow A^{q+} + H(m), q \gt 3, m \gt n $$
    !+
    !+###References
    !+* Page 132 in Ref. 5 [[atomic_tables(module)]]
    !+* Page 134 in Ref. 5 [[atomic_tables(module)]]
    !+* Page 136 in Ref. 5 [[atomic_tables(module)]]
    !+* Page 138 in Ref. 5 [[atomic_tables(module)]]
    !+* Page 140 in Ref. 5 [[atomic_tables(module)]]
    !+* Page 142 in Ref. 5 [[atomic_tables(module)]]
    !+* Page 142 in Ref. 5 [[atomic_tables(module)]]
    !+* Page 144 in Ref. 5 [[atomic_tables(module)]]
    !+* Page 146 in Ref. 5 [[atomic_tables(module)]]
    !+
    real(Float64), intent(in)       :: eb
        !+ Collision energy [keV]
    integer, intent(in)             :: q
        !+ Ion charge
    integer, intent(in)             :: n
        !+ Initial atomic energy level/state
    integer, intent(in)             :: m
        !+ Final atomic energy level/state
    real(Float64)             :: sigma
        !+ Cross Section [\(cm^2\)]

    real(Float64), dimension(12) :: sigma_m

    sigma_m = Aq_excit_n(eb, q, n, 12)
    if(m.le.0) then
        sigma = sum(sigma_m)
    else
        sigma = sigma_m(m)
    endif

end function Aq_excit_n_m