Spectral Study of A¹Π–X¹Σ⁺ Transitions of CO Relevant to Interstellar Clouds

Abstract

Highly correlated ab initio calculations were performed for an accurate determination of the A 1Π–X 1Σ+ system of the CO molecule. A highly accurate multi-reference configuration interaction approach was used to investigate the potential energy curves (PECs) and the transition dipole moment curve (TDMC). The resultant PECs and TDMC found by using the aug-cc-pV5Z (aV5Z) basis set and 5330 active spaces are in good agreement with the experimental data. Moreover, the Einstein A coefficients, lifetimes, ro-vibrational intensities, absorption oscillator strengths, and integrated cross sections are calculated so that the vibrational bands include v″ = 0–39 v′ = 0–23. For applications in the atmosphere and interstellar clouds, we studied the transition lineshapes to Gaussian and Lorentzian profiles at different temperatures and pressures. The intensities were calculated at high temperature that was used to satisfy some astrophysical applications, such as in planetary atmospheres. The results are potentially useful for important SAO/NASA Astrophysics Data System and databases such as HITRAN, HITEMP, and the National Institute of Standards and Technology. Because the results from many laboratory techniques and our calculations now agree, analyses of interstellar CO based on absorption from A 1Π–X 1Σ+ are no longer hindered by present spectral parameters.

Measurements and modeling of CO 4th positive (A–X) radiation

“…DeLeon supplies an interpolation based on his experimental data and those previously reported by Field et al [31]. The ETMF of Kirby and Cooper [20], Chantranupong et al [22], Cheng et al [23] and Spielfiedel et al [21] are ab initio calculations. Figure 1 shows a comparison of the electronic transition moments.…”

“…The vibrational wavefunctions were then calculated. Finally, the electronic transition moment Re(r) was taken from one of five datasets reported in the literature: DeLeon [18,19], Kirby and Cooper [20], Spielfiedel et al [21], Chantranupong et al [22] and Cheng et al [23]. DeLeon supplies an interpolation based on his experimental data and those previously reported by Field et al [31].…”

“…The slit function has an approximate FWHM of 0.08 nm and is shown in Figure 11 for reference. Figures 12a -12d show the comparison between the measured spectrum and SPECAIR calculations based upon the ETMFs from Kirby [20], Chantranupong [22], Cheng [23] Fig. 9 and DeLeon [18,19].…”

“…Specifically, this paper compares the performance of five CO(4+) radiation models against the experimental data obtained in the VUV and identifies which models work best. The transition probabilities tested here are based on the electronic transition moment functions of DeLeon [18,19], Kirby and Cooper [20], Spielfiedel et al [21], Chantranupong et al [22] and Cheng et al [23]. [18,19], Kirby and Cooper [20], Spielfiedel et al [21], Chantranupong et al [22] and Cheng et al [23] For the analysis presented here, all experimental results are compared with simulations obtained using SPECAIR.…”

“…The transition probabilities tested here are based on the electronic transition moment functions of DeLeon [18,19], Kirby and Cooper [20], Spielfiedel et al [21], Chantranupong et al [22] and Cheng et al [23]. [18,19], Kirby and Cooper [20], Spielfiedel et al [21], Chantranupong et al [22] and Cheng et al [23] For the analysis presented here, all experimental results are compared with simulations obtained using SPECAIR. [24,25,26] The spectral positions of the CO(4+) lines are calculated with the Dunham expansion coefficients of Farrenq et al [27] and Simmons et al [28].…”