## 1 Introduction  
In crystal imaging systems of ITER [1; 2; 3] and CFETR [4], Xenon (Xe) is chosen as an externally injected diagnostic probe impurity for the diagnosis of ion temperature and toroidal plasma velocity [5]. The Ne-like Xe\({}^{44+}\) exhibits high concentrations across a wide range of electron temperatures. Its strong 3D [2p\({}^{6}\)-(2p\({}^{5}\)\({}_{3}\)/2d\({}_{5}\)/2d\({}_{5}\)/2)\({}_{1}\), 2.7203 A [6]] line serves as a valuable diagnostic tool in the core plasma [7]. Consequently, this ion has attracted considerable research attention, leading to extensive measurements in various experiments, including tokamaks [6; 8; 9; 10], EBITs [11; 12; 13; 14; 15; 16; 17], laser plasmas [18; 19; 20], and low-inductance spark devices [21]. Beyond the limitations of current diagnostic capabilities, the Ne-like Xe\({}^{44+}\) holds promise for an even broader diagnostic potential [22; 23; 24], thereby asking for more precise atomic parameters and sophisticated plasma models to refine spectral emission mechanisms. Ne-like ions, with their fully filled L-shell ground state, exhibit stability across a wide range of plasma temperatures and can emit exceptionally bright X-ray radiation that is easily observable. Consequently, the X-ray spectra emitted by these ions have been exploited for plasma diagnostics in high-temperature plasma, including magnetic confinement fusion [25; 26; 27; 28], inertial confinement fusion [29; 30; 31], and astrophysical plasma [32; 33; 34]. For instance, the brightest 3C and 3D lines emitted by the Ne-like Fe ion in the Sun and other stellar coronal spectra offer great potential for diagnosing density and temperature [35; 36; 37]. Nevertheless, the discrepancy between experimental and theoretical 3C/3D oscillator-strength ratios poses significant obstacles to their diagnostic application [38; 39; 40; 41; 42]. These inconsistencies raised concerns about the accuracy of the emission intensities from Ne-like ions, prompting extensive research efforts to resolve this problem [43; 44; 45]. Recently, [PERSON] et al. [46] conducted measurements with high resolving power and an exceptionally high signal-to-noise ratio, coupled with Voigt fitting to distinguish Lorentzian wings, leading to the determination of the oscillator-strength ratio and achieved excellent agreement with high-precision theoretical calculations. This study finally resolves the long-standing mystery surrounding oscillator strengths in the Ne-like Fe ion and provides valuable implications for improving the accuracy of experimental line-intensity ratio measurements. The variation of the 3C/3D oscillator strengths across the Ne-like isoelectronic sequence with respect to the atomic number Z provides an avenue to investigate various effects that contribute to the experimental-theoretical deviations, such as electron-correlation effects [47; 48; 49; 50; 51], population corrections [48; 52; 53; 54], and polarization [55; 56]. Recently, [PERSON] et al. [14] demonstrated that there is an apparent change in the 3C/3D line-intensity ratio at approximately Z = 54, attributed to the suppressed collision strength for the upper level of the 3D line due to strong configuration mixing with the upper level of the adjacent 3F {2p\({}^{6}\)-(2p\({}^{5}\)\({}_{1}\)/2\({}_{3}\)s\({}_{1}\)/2\({}_{J}\)=1, 2.7288 A [6]} line. That strong mixing is associated with level crossing, which arises from the diminishing importance of Coulomb potential relative to relativistic and quantum electrodynamical (QED) effects with increasing atomic number. This also usually implies a transition from _LS_ to _jj_ coupling schemes and brings about a significant rearrangement of atomic structures. [57]. In the present case, Ne-like Xe\({}^{44+}\) (Z = 54) is in the vicinity of level crossing between the upper levels of the 3F and 3D lines. As the atomic number over Z = 55, the upper level of the 3F line surpasses that of the 3D line.