FAME now accepts exponential down parameter as power function.

In recent literature it is common to account for the temperature dependence
of the exponential down parameter with a simple power law of the form

dEdown = alpha * (T / T0)^n

Often the value of n is 0.8-1.0, which implies a pretty significant
temperature effect. This commit enables FAME to read and use the
three-parameter power law expression above.

source/fame/io.f90

@@ -146,20 +146,30 @@ subroutine readInput(net, Tlist, Plist, Tmin, Tmax, Pmin, Pmax, &
         line = readMeaningfulLine()
         call getFirstToken(line, token)
         if (index(token, 'singleexpdown') /= 0) then
-            call processQuantity(line, units, net%bathGas%dEdown)
+            ! Next three lines are alpha, T0, and n
+            line = readMeaningfulLine()
+            call processQuantity(line, units, net%bathGas%dEdown%alpha)
             if (index(units(1:6), 'kj/mol') /= 0) then
-                net%bathGas%dEdown = net%bathGas%dEdown * 1000
+                net%bathGas%dEdown%alpha = net%bathGas%dEdown%alpha * 1000
             elseif (index(units(1:7), 'cal/mol') /= 0) then
-                net%bathGas%dEdown = net%bathGas%dEdown * 4.184
+                net%bathGas%dEdown%alpha = net%bathGas%dEdown%alpha * 4.184
             elseif (index(units(1:8), 'kcal/mol') /= 0) then
-                net%bathGas%dEdown = net%bathGas%dEdown * 4184
+                net%bathGas%dEdown%alpha = net%bathGas%dEdown%alpha * 4184
             elseif (index(units(1:5), 'cm^-1') /= 0) then
-                net%bathGas%dEdown = net%bathGas%dEdown * 2.9979e10 * 6.626e-34 * 6.022e23
+                net%bathGas%dEdown%alpha = net%bathGas%dEdown%alpha * 2.9979e10 * 6.626e-34 * 6.022e23
             elseif (index(units(1:5), 'j/mol') == 0) then
-                write (0, fmt='(a)') 'Invalid units for single exponential down parameter.'
+                write (0, fmt='(a)') 'Invalid units for single exponential down alpha parameter.'
+                stop
+            end if
+            line = readMeaningfulLine()
+            call processQuantity(line, units, net%bathGas%dEdown%T0)
+            if (index(units(1:5), 'k') == 0) then
+                write (0, fmt='(a)') 'Invalid units for single exponential down T0 parameter.'
                 stop
             end if
-            write (1,fmt=*) "dEdown =", net%bathGas%dEdown, "J/mol"
+            line = readMeaningfulLine()
+            call getFirstToken(line, token)
+            read(token, *), net%bathGas%dEdown%n
         else
             write (0, fmt='(a)') 'Invalid collisional transfer probability model specification. Should be "SingleExpDown".'
             stop

source/fame/network.f90

@@ -10,11 +10,18 @@ module NetworkModule
 
     implicit none
 
+    ! dEdown = alpha * (T / T0)^n
+    type DeltaEDown
+        real(8) :: alpha
+        real(8) :: T0
+        real(8) :: n
+    end type
+
     type GeneralData
         real(8) :: molWt    ! The molecular weight of the bath gas in kg/mol
         real(8) :: sigma    ! The Lennard-Jones sigma parameter of the bath gas in m
         real(8) :: eps      ! The Lennard-Jones epsilon parameter of the bath gas in J
-        real(8) :: dEdown   ! Average energy transferred in a deactivating collision in J/mol
+        type(DeltaEDown) :: dEdown   ! Average energy transferred in a deactivating collision in J/mol
     end type
 
     type SpectralData
@@ -1054,7 +1061,7 @@ subroutine network_applyApproximateMethod(net, nIsom, nReac, nProd, &
         end do
 
         ! Average energy transferred in a deactivating collision
-        dEdown = net%bathGas%dEdown
+        dEdown = net%bathGas%dEdown%alpha * (T / net%bathGas%dEdown%T0) ** net%bathGas%dEdown%n
 
         if (method == 1) then ! Modified strong collision