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A question about phosphorescence lifetime

Posted: 08 Feb 2020, 09:58
by linqiaosong
Last night, I calculated the phosphorescence response of the HF molecule using Dalton2019.alpha, and got the phosphorescence lifetime of the HF molecule. However, there is a question I wanna ask...The output information is following:

Code: Select all

 Phosphorescence transition rate from excited state no.  1
 (Triplet->singlet transition, high-temperature limit)

 Transition energy:  8.737 eV
    or   141.915 nm

  Length gauge: 
 Partial rates (H_SO): X-polarization 1.45786E+05 Transition moment :  1.434E-02
  Length gauge: 
 Partial rates (H_SO): Y-polarization  0.0000     Transition moment :   0.00    
  Length gauge: 
 Partial rates (H_SO): Z-polarization  9494.0     Transition moment :  3.660E-03

  Phosphorescence - length gauge: 
 Oscillator strength (/2PI)     (H_SO)    7.461901E-06
 Dipole strength [a.u.]         (H_SO)    2.190450E-04
 Dipole strength E-40 [esu**2 cm**2]      1.415134E+01
 Total transition rate          (H_SO)    5.175992E+04 s-1
 Total phosphorescence lifetime (H_SO)    1.931997E-05 s
As we all known, the lifetime of phosphorescence is following the formula: lifetime(s)=1.5/(Oscillator strength * (Transition energy(cm-1))^2)
If we use the result of output file, we will find that: lifetime=1.5/((7.461901E-06)*(2*PI)*(1/(141.915E-7)^2))=6.44345082456349E-06 s, which is the 1/3 of 1.931997E-05 s. What's more, we found that this phenomenon is common. Thus, I wanna know this factor 1/3 is the bug or the feature of Dalton Program? :?:

The input and output files are following:

Re: A question about phosphorescence lifetime

Posted: 10 Feb 2020, 10:15
by olav
Dear Qiaosong
For transitions between non-degenerate states, the general rule for the total transition rate is to average initial states and sum over final states. In the most common picture with a T->S transition, an ensemble average over the triplet states,assuming they are equally populated, shows up as a factor 1/3


Re: A question about phosphorescence lifetime

Posted: 10 Feb 2020, 11:03
by linqiaosong
Thank you very much for your answer