Ab initio study of the second positive system of N2 at high temperature

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The potential energy-curves (PECs) and electronic transition dipole moment-curves (TDMCs) of the B3Пg and C3Πu states of N2 have been investigated by employing the multi-reference configuration interaction (MRCI) approach with the augmented correlation consistent polarized valence quintuple-zeta (aV5Z) set and active spaces 31103110. The calculated PEs of the two states (B3Πg, C3Πu) agree well with the Rydberg-Klein-Rees (RKR) potential energy, and the calculated TDMCs are more precise than those reported in previous literature studies. Calculation of the Einstein A coefficients, spectral parameters and wavelengths by using the exact potential energy and dipole moment are consistent with the recent experimental and literature values. For the first time, the intensities of eight bands of the second positive system (2PS) of N2 are obtained from the summation of their respective absorption spectral line intensities. The absorption spectral intensities of the 0–0, 0–1, 2–0, 2–1, 3–0, 3–1, and 4–0, 4–1 bands were computed in a wide temperature range, especially at high temperatures. For example, the 0–0 band intensities are 4.58 × 10−15 cm−1/(molecule cm−2), 2.50 × 10−15 cm−1/(molecule cm−2) and 9.47 × 10−16 cm−1/(molecule cm−2) at 300 K, 3000 K, and 6000 K, respectively. These results of spectral intensities can be utilized to predict spectral characteristics, and also definited as a theoretical reference value for high temperature astrophysics.