Potential energy curves and UV absorption cross-sections of sulfur dimer

MRCI-F12+Q/aug-cc-pV(5+d)Z ab initio potential energy and transition dipole moment curves of three S2 electronic states: X^3\Sigma_g^-, B''^3\Pi_u (both x,y degeneracies), B^3\Sigma_u^-.

In addition, absorption cross-sections are included for four isotopologues (32S32S, 33S32S, 34S32S, and 36S32S) at T=300K. Additional two absorption cross-sections are included for 32S32S at T=370K and 823K for comparison with experimental cross-sections produced by Stark et al., J. Chem. Phys. 148, 244302 (2018).

The absorption cross-sections are in cm^2 and the wavelength is in nm. Potential energy curves are in Hartree and interatomic distance is in Aangstrom.

For linelists, the filename convention is used as follows:
discrete_[excited electronic state e]_[ground electronic v]_[ground electronic J].dat
for all discrete transitions from the specific v,J state to e. Indices are 0: B''^3Pi_ux; 1: B''^3Pi_uy; 2: B^3sigma_u^-

The linelist contents are displayed in two main columns:
[Energy (Hartree), Cross-section (cm^2)]
and for the B^3sigma_u^- state, i.e. discrete_2_i_j.dat files:
[Energy (Hartree), Cross-section (cm^2), Gamma (cm^-1)]
where Gamma is the pre-dissociation FWHM broadening factor for states with energy greater than the dissociation energy for B''^3Pi_u state.

The factor Gamma is calculated according to the close-coupling method shown in van Dischoeck et al. (1984), https://doi.org/10.1063/1.447622.

However, we are not certain with the complete accuracy of it, since we have not included spin-orbit coupling interactions, which is expected to have an effect on the pre-dissociation factor.

continuum_[excited electronic state e]_[ground electronic v]_[ground electronic J].dat
for evenly spaced continuum transitions from the specific v,J state to e. Indices are 0: B Pi_ux; 1: B Pi_uy; 2: B_sigma_u
[Energy (Hartree), Cross-section (cm^2)]

gnd_energies.dat
for all ground state v, J levels
[v, J, Energy (Hartree)]

The attached python script total_csection.py can be used to reproduce the total absorption cross-sections from linelists for each isotopologue by renaming the linelist directory to 'results' and putting in the same working directory as the script. Invoking the script, e.g.:
>>python3 total_csection.py --recalc --temp 300 --isos 32S 32S
will produce the total absorption cross-section with Boltzmann distribution and Doppler broadening at 300 Kelvin for 32S32S molecule.

MRCI-F12+Q/aug-cc-pV(5+d)Z 基于从头算的势能和跃迁偶极矩曲线，描述了三种 S2 电子态：X^3Sigma_g^-, B''^3Pi_u（包括 x, y 线性简并），B^3Sigma_u^-。

此外，还包括了四种同位素异构体（32S32S, 33S32S, 34S32S, 和 36S32S）在 T=300K 下的吸收截面。对于 32S32S，还包括了在 T=370K 和 823K 下的两个吸收截面，以便与 Stark 等人（J. Chem. Phys. 148, 244302，2018）产生的实验截面进行比较。

吸收截面以平方厘米为单位，波长以纳米为单位。势能曲线以哈特里为单位，原子间距以埃为单位。

对于谱线表，文件命名规范如下：
discrete_[激发电子态 e]_[基态电子 v]_[基态电子 J].dat，用于从特定 v, J 态到 e 的所有离散跃迁。索引为 0: B''^3Pi_ux；1: B''^3Pi_uy；2: B^3sigma_u^-。

谱线表内容展示在两列主要栏目中：[能量（哈特里），截面（平方厘米）]，对于 B^3sigma_u^- 态，即 discrete_2_i_j.dat 文件：[能量（哈特里），截面（平方厘米），伽马（cm^-1）]，其中伽马是对于能量大于 B''^3Pi_u 状态解离能的态的预解离全宽度展宽因子。

伽马因子根据 van Dischoeck 等人（1984）提出的紧耦合方法计算，可参见 https://doi.org/10.1063/1.447622。

然而，我们对其完全准确性持怀疑态度，因为我们没有包括自旋-轨道耦合相互作用，这预计会对预解离因子产生影响。

continuum_[激发电子态 e]_[基态电子 v]_[基态电子 J].dat，用于从特定 v, J 态到 e 的均匀分布连续跃迁。索引为 0: B Pi_ux；1: B Pi_uy；2: B_sigma_u。

[能量（哈特里），截面（平方厘米）]
gnd_energies.dat，用于所有基态 v, J 能级
[v, J, 能量（哈特里）]

附加的 python 脚本 total_csection.py 可用于从谱线表中重现每个同位素异构体的总吸收截面，通过将谱线表目录重命名为 'results' 并将其置于与脚本相同的工 作目录中。例如，调用脚本：

>>python3 total_csection.py --recalc --temp 300 --isos 32S 32S
将在 300 开尔文下为 32S32S 分子产生具有玻尔兹曼分布和多普勒展宽的总吸收截面。