Proton-impact transition data for c_6

[Chamani Gunasekera]

Hello CHIANTI Community,

I require the proton-impact collisional data from c_6.psplups to find the proton-impact collision rate coefficients. What is the data structure for the .psplups files?

I followed the Burgess & Tully type scaling detailed in the Chianti review of the proton rates found in the following paper https://ui.adsabs.harvard.edu/abs/2003ApJS..144..135Y/abstract.

Which states that y = log (C_ij), where y is the data in the .psplups file and C_ij are the proton collision rate coefficients. 

I compared these proton rates for the transition 2p1/2 - 2p3/2 (i.e. transition 3 -> 4) in c_6 to the ones in Zygelman & Delgarno (1986), which I have attached to this email. What is causing the discrepancy we see in the plot?

Thank you for your time,

Chamani M. Gunasekera

[will.t...@gmail.com]

Hi Chamani,

I think part of the issue here is the kind of scaling you are applying to the c_6.psplups data. The c_6.pslups data use y=C_ij, rather than y=log(C_ij).

The columns in the psplups files are, from L to R, the lower level of the transition, the upper level of the transition, the Burgess & Tully (B&T) scaling type, the oscillator strength, the energy spacing between the levels, and the B&T scaling parameter (denoted as C in the B&T paper or a in Eq. 5 of Young et al., 2003). The remaining columns are the scaled collision rate (y in the B&T paper). As noted in Section 2.2 of Young et al. (2003), the scaled collision rate can either have 5 or 9 points, depending on the ion and the type of scaling applied.

Looking at the c_6.psplups file,

  3  2  2 0.000e+00 2.384e-04 4.870e+03 5.450e-02 6.973e-02 4.379e-02 4.146e-02 1.745e-02
  2  4  2 0.000e+00 4.089e-03 2.970e+03 1.950e-04 1.268e-02 1.878e-02 1.935e-02 1.731e-02
  3  4  2 0.000e+00 4.328e-03 1.490e+03 1.627e-03 3.342e-03 3.590e-03 2.606e-03 1.017e-03

Note that the 3->4 transition (the last row) has a scaling type of 2 (y=C_ij, Eq. 28 of B&T) rather than a scaling type of 6 (y=log(C_ij), Eq. 6 of Young et al. 2003).

I hope that is helpful.

Best,

Will

[Young, Peter R. (GSFC-6710)]

Hi Chamani,

 

Apologies for not responding earlier, but thanks to Will for replying today. I looked into the c_6 data, and I also find a problem although different to what you found. I’ve attached a plot showing the comparison between Zygelman & Dalgarno (red) and CHIANTI (blue) for the three transitions. CHIANTI is clearly higher in all cases.

 

The ratio between the two is very close to 6^6. Z&D applied a Z^3 scaling to their rates, so it looks like we multiplied by Z^3 instead of dividing. I’ll confirm that this is the case, and then get the file updated. We’ll also need to check the other ions in the sequence.

 

Thanks, Peter

Thank you for your time,

Chamani M. Gunasekera

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[Chamani Gunasekera]

Dear Peter & Will,

Thanks so much for your replies. That makes a lot of sense now. Just one last question. What x-values for the temperature in B&T are you inferring in the c_6.psplups file? Is it x in the range (0, 0.9) for 5 spline points, as mentioned in Section 2.2 of Young et al. (2003).

Have a nice day,

Chamani

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[Young, Peter R. (GSFC-6710)]

Hi Chamani,

 

The spline values in the .psplups file are defined for x=0, 0.25, 0.50, 0.75 and 1.0 using the notation of Burgess & Tully (1992). So when you want the rate at a specific temperature, the temperature is converted to x using Eq. 27 of B&T, and then we run a spline through the points to get the upsilon at that value.

Thank you for your time,

Chamani M. Gunasekera

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