Discontinuity in NASA polynomials

[cfgold]

I computed Delta H_{rxn}(T) for CH3 + C2H5 -> CH4 + C2H4JJ. This Delta H has a discontinuity at ~1000 K, and it is ~ 0.5 kcal/mol (so not huge, but also not insignificant).

It is my understanding the the NASA coefficients are determined in GATPfit, which first uses a Wilhoit polynomial to compute Cp(T), then fits the NASA coefficients to these computed values. GATPfit includes a constraint that the polynomial be smooth at the intermediate temperature. However, if a large number of Cp(T) are reported, then the smoothness constraints are not necessarily met.

To improve the smoothness, the three constraints need to be weighted. If they already are being weighted, then the weighting factor needs to be increased.

[gmagoon]

Hmm...interesting. The constraints should be strictly enforced so there should be no weighting involved. I'm wondering if the discrepancy may be due to the fact that the intermediate temperature specified to GATPFit (1000 K) is not exactly equal to the one it uses (~995 K, based on one of the sampled points). Could you maybe post the coefficients in Chemkin format that RMG is giving?

[cfgold]

Here are the results from the get thermo thingy: ChemFormula: CH3J 1 C 1 {2,S} {3,S} {4,S} 2 H 0 {1,S} 3 H 0 {1,S} 4 H 0 {1,S}

The number of resonance isomers is 0 The NASA data is !Estimated by RMG using Group Additivity SPC(1) C 1H 3 G 300.000 5000.000 995.043 1 4.09369738E+00 3.70663607E-03-1.11169717E-06 1.61150833E-10-8.99672583E-15 2 1.60153864E+04-1.33623864E+00 3.94354223E+00-3.06983615E-04 1.18990784E-05 3 -1.32192644E-08 4.52441835E-12 1.62738470E+04 5.36012899E-01 4

ThermoData is 34.809999999999995 46.36977393464385 9.14 10.18 10.81 11.34 12.57 13.71 15.2 symmetry number = 6 CH3J H=34.809999999999995

Created new species: molecule(2) ChemFormula: C2H5J 1 C 1 {2,S} {3,S} {4,S} 2 C 0 {1,S} {5,S} {6,S} {7,S} 3 H 0 {1,S} 4 H 0 {1,S} 5 H 0 {2,S} 6 H 0 {2,S} 7 H 0 {2,S}

The number of resonance isomers is 0 The NASA data is !Estimated by RMG using Group Additivity SPC(2) C 2H 5 G 300.000 5000.000 995.043 1 4.27880081E+00 1.19981329E-02-3.55250933E-06 4.87152377E-10-2.56198285E-14 2 1.21442406E+04 1.24707240E+00 3.60910266E+00-2.37331109E-03 4.38349400E-05 3 -4.84958919E-08 1.66111194E-11 1.31222575E+04 8.71939931E+00 4

ThermoData is 28.599999999999987 59.86977393464385 11.73 14.469999999999999 17.05 19.339999999999996 23.02 25.91 31.529999999999998 symmetry number = 6 C2H5J H=28.599999999999987

Created new species: molecule(3) ChemFormula: C2H4JJ 1 C 1 {2,S} {3,S} {4,S} 2 C 1 {1,S} {5,S} {6,S} 3 H 0 {1,S} 4 H 0 {1,S} 5 H 0 {2,S} 6 H 0 {2,S}

The number of resonance isomers is 1 The NASA data is !Estimated by RMG using Group Additivity SPC(3) C 2H 4 G 300.000 5000.000 995.043 1 3.69785809E+00 9.96441823E-03-2.43262762E-06 2.58520878E-10-9.88335973E-15 2 3.72197731E+04 6.51828349E+00 3.39869264E+00-1.24726194E-04 2.97985178E-05 3 -3.27405155E-08 1.11463189E-11 3.78383143E+04 1.07690452E+01 4

ThermoData is 77.59999999999998 61.90814965668217 11.08 13.259999999999998 15.3 17.099999999999994 20.0 22.28 27.9 symmetry number = 8 C2H4JJ H=77.59999999999998

Created new species: molecule(4) ChemFormula: CH4 1 H 0 {2,S} 2 C 0 {1,S} {3,S} {4,S} {5,S} 3 H 0 {2,S} 4 H 0 {2,S} 5 H 0 {2,S}

The number of resonance isomers is 0 The NASA data is !Estimated by RMG using Group Additivity SPC(4) C 1H 4 G 300.000 5000.000 995.043 1 2.02228410E+00 9.28229267E-03-3.16423748E-06 4.94658495E-10-2.90486314E-14 2 -1.01179484E+04 7.96505034E+00 4.11128886E+00-6.44087023E-03 3.15810191E-05 3 -3.01829315E-08 9.53744383E-12-1.01710249E+04-2.80508476E-01 4

ThermoData is -17.9 44.47249048687124 8.43 9.84 11.14 12.41 15.0 17.25 20.63 symmetry number = 12 CH4 H=-17.9

[cfgold]

Oh it looks like the formatting is all out of whack. I'll send it to you later. -F

[rwest]

if he hit's the 'edit' link he'll be able to copy the originally formatted stuff. (or you can wrap it with <pre>tags</pre>

[cfgold]

Oops, quick mistake. The discontinuity was for the reaction on the singlet PES: CH3 + C2H5 -> CH4 + C2H4. C2H4 data is below: Created new species: molecule(6) ChemFormula: C2H4 1 C 0 {2,D} {3,S} {4,S} 2 C 0 {1,D} {5,S} {6,S} 3 H 0 {1,S} 4 H 0 {1,S} 5 H 0 {2,S} 6 H 0 {2,S}

The number of resonance isomers is 0 The NASA data is !Estimated by RMG using Group Additivity SPC(6) C 2H 4 G 300.000 5000.000 995.043 1 4.84788803E+00 9.04790364E-03-2.91089165E-06 4.34058759E-10-2.45509522E-14 2 3.91107645E+03-5.09518204E+00 3.80813213E+00-7.07638893E-03 5.20038258E-05 3 -5.68649861E-08 1.95238275E-11 5.12315836E+03 4.96671815E+00 4

ThermoData is 12.52 52.465433104454775 10.2 12.72 15.02 17.0 20.14 22.54 26.38 symmetry number = 4 C2H4 H=12.52

[cfgold]

Err, never mind. Mike found a bug in my code.