Evaluation report for the optical oscillator strength and generalized oscillator strength

　

Lin-Fan Zhu

　

There are two most commonly used methods to investigate the absolute optical oscillator strengths (OOS’s) for valence shell excitations, i.e., the photoabsorption method based on the Beer-Lambert law and the electron impact method. However, it is well known that the photoabsorption method based on the Beer-Lambert law has the line-saturation effect, and the measured OOS’s for the discrete transitions are lower than the true values. The situation will be severe for the discrete transitions with a very narrow natural width and large cross-section. So the data of the absolute OOS’s determined by the electron impact method are recommended when they are available.

The generalized oscillator strengths (GOS’s) can be measured by fast electron energy loss spectrometer when the first Born approximation is valid. However, the GOS data are fragmental because of the low cross section for fast electron impact and the difficulty to achieve enough energy resolution.

 

I. OOS’s and GOS’s for N₂

The previous investigations of OOS’s of N₂ up to 1993 have been summarized by Chan et al. [1]. Their measurement was carried out with the high resolution (0.048 eV fwhm) dipole (e, e) spectroscopy at the impact energy 3000 eV. The absolute scale was obtained by TRK sum-rule normalization. As mentioned above, their data are recommended.

The GOS’s for two forbidden transitions, i.e.,  and , in N₂ have only been measured by Skerbele and Lassettre [2] at the incident electron energies of 300, 400 and 500 eV, and small scattering angles of . So their results are adopted.

 

II. OOS’s for NO

  The previous investigations of OOS’s of NO up to 2002 have been summarized by Zhu et al. [3]. In their works, the absolute OOS’s for the vibrationally resolved, ,   and  bands have been determined with an incident electron energy of 2500 eV and an energy resolution of 55 meV. Meanwhile, the data of Zhu et al. [3] agree well with that of Chan et al. [4]. So we recommend the experimental OOS’s of Zhu et al. [3].

 

III. OOS’s for H₂

The previous investigations of OOS’s up to 1999 have been summarized by Zhong et al. [5]. Their measurement was carried out with the high resolution dipole (e, e) spectroscopy at the impact energy of 1500 eV. Considering the agreement between the experimental results of Refs. [5-7] and the theoretical calculation [5], the experimental results of Zhong et al. [6] are recommended.

 

Ⅳ.OOS’s and GOS’s for O₂

   The previous investigations of OOS’s of O₂ up to 1993 have been summarized by Chan et al. [8]. Their measurement was carried out with the high resolution (0.048 eV fwhm) dipole (e, e) spectroscopy at an impact energy of 3000 eV. The absolute scale was obtained by TRK sum-rule normalization. Considering the agreement between the experimental results of Refs. [8-9] and the energy resolution, we recommend the experimental OOS’s of Chan et al. [8].

  The absolute GOS’s for Schumann-Runge continuum ane , have only been reported by Newell et al [10] at the incident electron energies of 100, 200, 300, 400 and 500 eV with the scattering angle region of . So their results are adopted.

 

Ⅴ.  OOS’s for HCl

The OOS’s of HCl have recently been measured by Li et al. [11] using high resolution dipole (e, e) method with an incident electron energy of 2500 eV. To the best of our knowledge, this is the only measurement of OOS’s of HCl by electron impact method. The photoabsorption method has also been used to determine OOS’s of HCl [12-16]. But this method based on the Beer-Lambert law has the limitation of the line-saturation effect, so the OOS’s of Li et al. [11] are recommend.

 

[1]      W. F. Chan, G. Cooper, R. N. S. Sodhi and C. E. Brion, Chem.Phys. 170, 81(1993) and the references therein

[2]      A. Skerbele and E. N. Lassettre, J. Chem. Phys. 53, 3806(1970)

[3]      L. F. Zhu, Z. P. Zhong, Z. S. Yuan, W. H. Zhang, X. J. Liu, X. M. Jiang, L. Z. Xu and J. M. Li, Chin. Phys. 11, 1149(2002) and the references therein

[4]      W. F. Chan, G. Cooper and C.E. Brion, Chem.Phys. 170, 111(1993)

[5]      Z. P. Zhong, W. H. Zhang, K. Z. Xu, R. F. Feng, and J.M. Li, Phys. Rev. A 60, 236(1999)

[6]      Z. P. Zhong, K. Z. Xu, R. F. Feng, X. J. Zhang, L. F. Zhu，X. J. Liu, J. Electro. Spec. Relat. Phenom., 94, 127 (1998)

[7]      W. F. Chan, G.. Cooper and C. E. Brion, Chem. Phys. 168,  375(1992)

[8]      W. F. Chan, G. Cooper and C. E. Brion, Chem. Phys.170, 99(1993)

[9]      L. F. Zhu, Z. P. Zhong, Q. Ji, X. J. Zhang, S. L. Wu, R. F. Feng, K. Z. Xu, Acta Physica Sinica 46, 458 (1997)

[10]  W. R. Newell, M. A. Khakoo and A. C. H. Smith, J. Phys. B: At. Mol. Opt. Phys. 13, 4877 (1980)

[11]  W. B. Li, L. F. Zhu, X. J. Liu, Z. S. Yuan, J. M. Sun, H. D. Cheng, Y. Sakai and K. Z. Xu, Chin. Phys. Lett. 20, 2152(2003)

[12]  P. L. Smith, K. Yoshino, J. H. Black and W. H. Parkinson, Astrophys. J. 238, 874(1980)

[13]  E. C. Y. Inn, J. Atm. Sci. 32, 2375(1975)

[14]  J. B. Nee, M. Suto and L. C. Lee, J. Chem. Phys. 85, 719(1986)

[15] M. Bahou, C. Y. Chung, Y. P. Lee, B. M. Cheng, Y. L.Yung and L. C. Lee, Astrophys. J. 559 L179(2001)

[16] B. M. Cheng, C. Y. Chung, M. Bahou, Y. P. Lee and L. C. Lee, J. Chem. Phys. 17, 4293(2002)