外电场作用下对光气分子的理化性质研究
Study on the Physicochemical Properties of Phosgene Molecules Under an External Electric Field

摘要：光气（COCl₂），一种无色剧毒气体，工业中使用的氯化溶剂会迅速衰变成光气，对环境产生污染。研究性质和解离方法对减少污染具有重要价值。本文基于密度泛函理论（DFT）在BPV86/6-311G+（2d，p）水平上研究了在外加电场（0~12.855V∙nm^-1）作用下COCl₂的物理和化学性质，包括键长，总能量，电偶极矩，LUMO-HOMO能隙，红外光谱，拉曼光谱，解离势能面以及激发态等。当外加电场增大时，红外光谱和拉曼光谱均出现红移和强度变化。采用BPV86/6-311G+（2d，p）沿C=O键扫描单点能量得到势能曲线，通过拟合外加电场下势垒的线性曲线，得到解离特性表现为解离势垒逐渐减小，并计算了零势垒对应的场。此外，采用TD-SCF/6-311G+（2d，p）的方式得到COCl₂的紫外-可见光谱随着外加电场增大逐渐红移，激发能总体呈下降趋势。研究的结果为对COCl₂的深入研究提供了重要理论基础，体现了光气分子在外部电场下结构和性质的显著变化，为降解COCl₂以实现可持续发展提供了重要理论依据。
Abstract: Phosgene (COCl₂), a colorless and highly toxic gas, is rapidly degraded from chlorinated solvents used in industry, causing environmental pollution. Studying its properties and dissociation methods holds significant value for pollution reduction. This paper investigates the physical and chemical properties of COCl₂ under external electric fields (0–12.855 V·nm⁻¹), including bond lengths, total energy, electric dipole moment, LUMO-HOMO energy gap, infrared spectra, Raman spectra, dissociation potential energy surfaces, and excited states, based on density functional theory (DFT) at the BPV86/6-311G+(2d,p) level. As the external electric field increases, red shifts and intensity variations are observed in both infrared and Raman spectra. The potential energy curve obtained by scanning single-point energy along the C=O bond using BPV86/6-311G+(2d,p) reveals a gradual decrease in dissociation barriers through linear fitting, and the critical field corresponding to zero barrier is calculated. Additionally, TD-SCF/6-311G+(2d,p) results show that the ultraviolet-visible spectra of COCl₂ exhibit red shifts and overall declining excitation energies with increasing electric fields. These findings provide a theoretical foundation for in-depth studies of COCl₂, highlighting significant structural and property changes under external electric fields, and offer critical insights for degrading COCl₂ to achieve sustainable development.

关键词：光气，外加电场，密度泛函理论，解离
Keywords: Phosgene; External electric field; Density functional theory; Dissociation

1.引言
1. Introduction

光气，化学名称为碳酰氯，化学式为COCl₂,是一种剧毒气体，可诱发急性窒息性毒性反应，临床表现包括呼吸道刺激、肺水肿、呼吸窘迫综合征及多器官功能衰竭^[1-3]，其军事应用历史可追溯至第二次世界大战期间，曾被作为化学武器使用。作为关键化学中间体，该化合物在农药合成、异氰酸酯基聚合物制备、染料工程及制药工业中具有不可替代的作用^[4]。工业储存条件下，光气以液态形式存在（沸点7.56°C），在标准环境温度（20°C）下饱和蒸气压达161.6kPa。当液态光气泄漏至大气中时，会迅速蒸发，形成白色烟雾状气团，且由于其密度大于空气，气团会贴近地面扩散，对人类的健康造成威胁。尽管工业化安全处理技术发展逾百年，2017年全球年产量仍维持在108万吨量级^[5]。该物质在常温常压下呈无色气态，水溶性较低（25°C时溶解度0.022 g/100 mL），但易溶于苯、氯仿等有机溶剂。热力学研究表明，在湿润环境及温度超过300°C条件下，光气发生分解反应生成CO₂、CO及HCl，其低水溶性导致降解过程需经历水解中间步骤，显著增加环境治理难度
Phosgene, chemically known as carbonyl chloride (COCl₂), is a highly toxic gas that induces acute asphyxiant toxicity, manifesting clinically as respiratory irritation, pulmonary edema, acute respiratory distress syndrome, and multi-organ failure. Historically employed as a chemical weapon during World War II, it remains an indispensable chemical intermediate in pesticide synthesis, isocyanate polymer production, dye engineering, and pharmaceutical industries. Under industrial storage conditions, phosgene exists as a liquid (boiling point: 7.56°C) with a saturated vapor pressure of 161.6 kPa at standard ambient temperature (20°C). Liquid phosgene leakage rapidly evaporates, forming white fog-like plumes that diffuse along ground surfaces due to higher density than air, posing severe health risks. Despite century-long advancements in industrial safety protocols, global production remained at 1.08 million tons annually as of 2017. The compound exhibits low water solubility (0.022 g/100 mL at 25°C) but high solubility in organic solvents like benzene and chloroform. Thermodynamic studies indicate decomposition into CO₂, CO, and HCl under humid conditions above 300°C, though its low aqueous solubility necessitates hydrolysis intermediates, significantly complicating environmental remediation.

现有检测体系已整合传感技术，包括电荧光生物传感器、压电传感器、半导体传感器、比色探针、石英晶体微天平、光谱分析法、透射电子显微镜、气相色谱、液相色谱和X-射线衍射^[6-14]，以及荧光探针法^[4]，然而，降解技术领域仍存在显著瓶颈，开发高效环境友好型降解方法已成为降低生态风险的关键研究方向。值得注意的是，光气消除工艺的优化被证实是绿色聚氨酯合成技术革新的核心环节^[15]。
Current detection systems integrate various sensing technologies including electro-fluorescent biosensors, piezoelectric sensors, semiconductor sensors, colorimetric probes, quartz crystal microbalances, spectroscopic analysis, transmission electron microscopy, gas chromatography, liquid chromatography, X-ray diffraction, and fluorescent probe methods. However, degradation technologies face significant bottlenecks, making the development of efficient environmentally friendly degradation methods crucial for ecological risk mitigation. Notably, optimization of phosgene elimination processes has been identified as pivotal for green polyurethane synthesis technology innovation.

本文从构建外加电场辅助降解的创新角度，基于密度泛函理论（DFT）（该理论已广泛运用于对分子结构及能量的分析，如韩博元对DMSO分子的理化性质研究^[16]以及于聪对HCFC-22分子的解离性研究^[17]），采用BPV86/6-311G+（2d，p）理论水平完成分子几何优化，定量表征COCl₂分子的理化性质，包括分子的键长，总能量，偶极矩和前沿分子轨道能级，同时对其红外光谱，拉曼光谱，紫外-可见光谱及其激发能进行分析，并通过沿C=O键扫描势能面，研究了COCl₂分子在电场作用下的解离，为发展新型光气降解技术提供了分子动力学基础和主要理论参考。
This study proposes an innovative approach of constructing an external electric field-assisted degradation system. Based on density functional theory (DFT) (which has been widely applied in molecular structure and energy analysis, as evidenced by Han Boyuan's research on physicochemical properties of DMSO molecules ^[16] and Yu Cong's investigation on HCFC-22 molecular dissociation ^[17] ), we performed molecular geometry optimization at the BPV86/6-311G+(2d,p) theoretical level. We quantitatively characterized the physicochemical properties of COCl ₂ molecules, including bond lengths, total energy, dipole moment, and frontier molecular orbital energy levels. Simultaneously, we analyzed their infrared spectra, Raman spectra, UV-Vis spectra, and excitation energies. By scanning the potential energy surface along the C=O bond, we investigated the dissociation of COCl ₂ molecules under electric fields. This work establishes molecular dynamics foundations and provides key theoretical references for developing novel phosgene degradation technologies.

理论与计算方法
Theoretical and Computational Methods
Theoretical and Computational Methods

在外加电场下，分子系统的哈密顿量H由（1）式给出
Under external electric fields, the Hamiltonian H of molecular systems is expressed as:
Under external electric fields, the Hamiltonian H of molecular systems is expressed as:

（1）

式中，H₀为无外电场时的哈密顿量，而H_int为电场与分子系统的相互作用哈密顿量函数。在偶极子近似下，相互作用哈密顿函数H_int可进一步由等式（2）得到
where H₀ represents the field-free Hamiltonian, and H₁ denotes the interaction Hamiltonian between the electric field and molecular system. Under dipole approximation, the interaction Hamiltonian H₁ can be further expressed by Equation (2):

（2）

式中，μ即为偶极矩，而F为外加电场强度矢量，本文中外加电场范围从0至12.855V∙nm^-1。
where μ is the dipole moment and F represents the external electric field intensity vector. The applied field range in this study spans 0–12.855 V·nm⁻¹.

本研究运用Gaussian 09量子化学软件包，系统评估了三种交换相关泛函（B3LYP、B3PW91、BPV86）与不同基组（6-311G（d，p）、6-311+G（d，p）、6-311G+（2d，p））对COCl₂基态结构的预测精度（表1）。通过对比实验晶体学数据（C-Cl键：1.766×10^-10 m，C=O键：1.181×10^-10 m）（该数据由美国国家标准与技术研究所（NIST）化学动力学数据库给出），BPV86泛函结合6-311G+（2d，p）基组展现出最优预测一致性：C-Cl键计算值为1.768×10^-10m（误差0.11%），C=O键计算值为1.184×10^-10 m（误差0.25%），显著优于B3LYP（C-Cl误差0.23%）和B3PW91（C-Cl误差1.02%）方法。
This study systematically evaluated the predictive accuracy of three exchange-correlation functionals (B3LYP, B3PW91, BPV86) combined with different basis sets (6-311G(d,p), 6-311+G(d,p), 6-311G+(2d,p)) for the ground-state structure of COCl₂ using the Gaussian 09 quantum chemistry software package (Table 1). By comparing with experimental crystallographic data (C-Cl bond: 1.766×10 ^-10 m, C=O bond: 1.181×10 ^-10 m) from the NIST Chemical Kinetics Database, the BPV86 functional with the 6-311G+(2d,p) basis set demonstrated optimal agreement: calculated C-Cl bond length of 1.768×10 ^-10 m (error 0.11%) and C=O bond length of 1.184×10 ^-10 m (error 0.25%), significantly outperforming the B3LYP (C-Cl error 0.23%) and B3PW91 (C-Cl error 1.02%) methods.

具体而言，B3LYP泛函在扩展基组（6-311+G（d，p））下的C-Cl键长误差仍达0.18%（1.764×10^-10 m），而BPV86泛函通过改进电子相关能描述，其键长预测误差降低至0.11%。此外，基组完备性对计算结果影响显著：含双重极化函数的6-311G+（2d，p）基组相较于单极化基组（6-311G（d，p）），将C=O键长误差从1.87%优化至0.25%，表明其对氯原子外层电子云的高效表征能力。优化后的分子结构（图1）经振动频率分析确认收敛于势能面极小点（无虚频），并以此为基础计算总能量、偶极矩及光谱性质。所有计算均采用严格收敛标准（能量阈值：10⁻⁸Hartree;力收敛：0.0003 Hartree/×10^-10 m），确保数值稳定性与物理合理性。通过与实验值比较得到相对误差，得出BPV86/6-311G+（2d，p）的方式优化与实验值最为一致。在后续实验中，本研究统一采用上述优化方法，系统获取了COCl₂分子的几何构型、总能量、红外光谱及解离势能面等关键参数
Specifically, the B3LYP functional still exhibits a C-Cl bond length error of 0.18% (1.764×10 ^-10 m) under the extended basis set (6-311+G(d,p)), while the BPV86 functional reduces this prediction error to 0.11% by improving the description of electron correlation energy. Furthermore, basis set completeness significantly impacts computational results: the 6-311G+(2d,p) basis set with double polarization functions optimizes the C=O bond length error from 1.87% to 0.25% compared to the single-polarization basis set (6-311G(d,p)), demonstrating its superior characterization capability for the outer electron cloud of chlorine atoms. The optimized molecular structure (Figure 1) was confirmed to converge at a minimum on the potential energy surface (no imaginary frequencies) through vibrational frequency analysis, forming the basis for calculating total energy, dipole moment, and spectral properties. All calculations employed stringent convergence criteria (energy threshold: 10⁻⁸ Hartree; force convergence: 0.0003 Hartree/×10 ^-10 m) to ensure numerical stability and physical rationality. Comparative analysis with experimental values revealed that the BPV86/6-311G+(2d,p) method achieves the best agreement. In subsequent experiments, this study systematically obtained key parameters of the COCl₂ molecule - including geometric configuration, total energy, infrared spectrum, and dissociation potential energy surface - using this optimized approach.

图1.优化后的COCl₂分子结构图，图示箭头为外加电场方向。
Fig. 1. Optimized molecular structure of COCl₂. Arrow indicates external electric field direction.

表1.不同优化方式下COCl₂分子的键长
Table 1. Bond lengths of COCl₂ under different optimization methods

结果和讨论
Results and Discussion

3.1外加电场对分子键长，总能量和电偶极矩的影响
3.1 Effects of External Electric Field on Molecular Bond Lengths, Total Energy, and Electric Dipole Moment

本研究在外加电场（0–12.855 V·nm^-1）作用下，基于BPV86/6-311G+（2d，p）理论方法优化COCl₂分子几何结构，定量表征电场强度对键长参数（C=O、C-Cl）、总能量及偶极矩的调控规律（表2）。
Using BPV86/6-311G+(2d,p), we systematically investigated electric field (0–12.855 V·nm⁻¹) effects on COCl₂'s geometric parameters (C=O, C-Cl bond lengths), total energy, and dipole moment (Table 2).

如图2所示，沿分子偶极矩方向施加电场时，C=O键长呈现1.184×10^-10 米→1.213×10^-10 m 的线性增长（ΔL=0.029 ×10^-10 m），而C-Cl键长则从1.768 ×10^-10 m收缩至1.738 ××10^-10 m（ΔL=0.030 ×10^-10 m），表明外场作用下C=O键解离倾向增强，C-Cl键稳定性提升。此现象源于电场诱导的分子内电荷重分布：C→O方向电子密度偏移削弱C=O键共价性，同时Cl→C电荷转移增强C-Cl键静电相互作用^[19]。此外，电场强度的增加导致分子内库仑势与外部电场的竞争效应，进一步加剧了键长的非线性响应^[20]。 

在外加电场（0–12.855 V·nm⁻¹）作用下，COCl₂分子总能量随场强增加呈递减趋势（图3），从-1033.930 Hartree降至-1033.910 Hartree（ΔE=0.020 Hartree），同时偶极矩则则持续增大，表明分子极性增强的同时体系稳定性提升。能量降低主要由哈密顿量中偶极-电场耦合项（-μ·F）驱动，其通过降低体系势能主导能量演化过程^[21]。
Total energy decreases monotonically from -1033.930 Hartree to -1033.910 Hartree (ΔE=0.020 Hartree) with increasing field strength (0–12.855 V·nm⁻¹), while dipole moment shows continuous enhancement (Fig. 3). Energy reduction primarily derives from dipole-field coupling term (-μ·F) in Hamiltonian, which dominates system stabilization through potential energy minimization.

表2不同外加电场下COCl₂键长、总能量和偶极矩对应的数值。
Table 2. Bond lengths, total energy, and dipole moment of COCl₂ under different electric fields.

图 2.C=O和C-Cl键在不同电场下的键长的变化。 

图3分子的能量和偶极矩在不同电场下的变化（1Debye=3.33564×10^-30C·m）。
Fig. 3. Variations of molecular energy and dipole moment under different electric fields (1 Debye = 3.33564×10⁻³⁰ C·m).

3.2外电场对COCl₂分子的轨道能级和能隙的影响
3.2 External Electric Field Effects on COCl₂ Molecular Orbital Energy Levels and Energy Gap

基于BPV86/6-311G+（2d，p）方法优化的COCl₂分子结构，本研究系统分析了外加电场（0–12.855V∙nm^-1）对最高占据分子轨道（HOMO）与最低未占分子轨道（LUMO）能级^{[21; 22]}，及其能隙的影响（表3）。计算结果表明，随着电场强度的增加，HOMO能量（E_H）从初始的-0.291 Hartree逐渐升高至-0.289Hartree（ΔE_H=0.002 Hartree），而LUMO能量（E_L）从-0.112Hartree显著降低至-0.126 Hartree（ΔE_L=-0.014 Hartree），导致HOMO-LUMO能隙（E_G=E_L-E_H）从0.178 Hartree大幅缩小至0.163 Hartree（ΔE_G=0.015 哈特里）。（本文中能量单位均用Hartree表示，1 Hartree=27.2 eV） 

从分子轨道理论角度分析，LUMO能级（E_L）表征分子接受电子的能力，其数值降低表明分子电子亲和势增强;同型（E_H）可定性反映其失去电子的能力，E_H的上升则反映其电子释放倾向的增强^[23]。HOMO-LUMO的能隙E_G为E_H和E_L之间的能量差，可以反映电子跃迁的能力，E_G的缩减现象表明电子激发所需能量显著降低^[24]。由式（3）可以计算得到E_G。 

（3）

如图4所示，随着外加电场强度的增大，E_L呈现显著下降趋势，EH仅以较低速率上升，表明电场对LUMO轨道的调控效应显著强于HOMO。同时E_G的持续减小也表明激发能阈值降低，电子从占据轨道向未占轨道跃迁所需的能量降低表明电场增大时，COCl₂分子在电场作用下的光化学反应活性呈增强趋势，证实电场可有效调控分子反应动力学。
Fig. 4 shows E_L decreasing more significantly than E_H increases, confirming stronger field modulation on LUMO. The persistent E_g reduction predicts UV-Vis spectral red shifts (λ∝1/E_g), aligning with experimental field-induced spectral shifts, providing theoretical basis for field-controlled degradation pathways.

能隙E_G的持续缩小不仅显著增强分子反应活性，还直接诱导电子吸收光谱将发生红移。根据能隙与吸收波长的反比关系（λ∝1/E_G），E_G的显著降低可能导致紫外-可见光谱的最强吸收峰红移。这一预测与实验中电场诱导分子光谱位移的普遍规律一致，为通过外场定向调控光气降解路径提供了理论依据。
The continuous E_g reduction not only enhances molecular reactivity but also induces red shifts in electronic absorption spectra. According to the inverse proportionality between energy gap and absorption wavelength (λ∝1/E_g), the significant decrease in E_g would lead to red shifts in UV-Vis absorption maxima, consistent with experimental observations of electric field-induced spectral displacements.

图4外电场作用下E_L，E_H和E_G的变化。 

表3外加电场下EL、EH和EG对应的能量数值。
Table 3. E_L, E_H, and E_g values under different electric fields.

3.3外加电场对COCl₂分子的红外吸收光谱的影响
3.3 External Electric Field Effects on COCl₂ Infrared Absorption Spectra

基于BPV86/6-311G+（2d，p）方法，本研究系统考察了外加电场（0–12.855V∙nm^-1）对COCl₂分子红外吸收光谱的影响。红外光谱的特征峰与分子振动模式一一对应，计算结果表明，COCl₂分子在无外加电场条件下存在6种特征振动模式。然而，其中三种特征峰的信号强度相对较弱，在红外光谱中未能显著呈现。为聚焦于可观测性较强的振动模式，本文选取特征峰强度较高的三种振动模式进行深入分析，其中频率为542.34 cm^-1的峰对应C-Cl键对称伸缩振动（C-Cl s-str，记为V1），频率为782.9 cm^-1的峰对应C-Cl键反对称伸缩振动（C-Cl a-str，记为V2），频率为1810.01 cm^-1的峰对应C=O键反对称伸缩振动（C=O a-str，记为V3），如表4所示。本研究的计算结果（表4）与美国国家标准与技术研究所（NIST）化学动力学数据库的基准数据^[18]（表5）表现出显著一致性，为所述方法的可靠性提供了理论支撑。 

在无外加电场条件下，V1、V2和V3振动模式如图5所示。当施加电场强度从0线性递增至12.855 V·nm⁻¹时，V1、V2和V3对应的频率的数据及变化记录在表4中。如图6所示，V1和V2振动模式均呈现显著红移，表明C-Cl键的振动能级降低，分子振动所需能量减少，键能减弱。
Under increasing fields (0–12.855 V·nm⁻¹), V1 and V2 exhibit significant red shifts (Fig. 5), indicating reduced vibrational energy levels and bond weakening. V3 intensity increases while V1/V2 intensities decrease, suggesting selective field effects: C-Cl bond destabilization versus C=O stabilization (Fig. 6).

进一步分析发现，V1和V2振动模式的强度随电场强度增加而显著降低，而V3振动模式的强度则逐渐升高。该现象揭示了外电场对C-Cl与C=O化学键的差异化调控机制：C-Cl键的极性增强，振动模式激发概率增大，键稳定性下降;而C=O键的振动模式则呈现稳定化趋势，键能增加。这种键选择性调控效应为光气降解提供了理论指导——通过定向施加外电场可优先削弱C-Cl键解离能，促进COCl₂分子的解离，同时维持C=O键的相对稳定，有效抑制高活性中间体的生成。 

表4外加电场作用下三种振动模式的频率的变化。
Table 4. Frequency variations of three vibrational modes under external electric fields.

表5美国国家标准与技术研究所化学动力学数据库（NIST）所给出的6种振动模式对应的频率。
Table 5. NIST Chemical Kinetics Database reference frequencies for six vibrational modes.

图5.三种振动模式在红外吸收光谱上所对应频率。
Figure 5. Corresponding frequencies of three vibration modes in the infrared absorption spectrum.

图6.不同外加电场下红外吸收光谱的变化。
Figure 6. Variations in infrared absorption spectra under different external electric fields.

3.4外加电场对COCl₂分子拉曼光谱的调控效应
3.4 Regulation Effect of External Electric Field on Raman Spectra of COCl₂ Molecules

基于BPV86/6-311G+（2d，p）方法，本研究系统分析了外加电场（0–12.855V∙nm^-1）对COCl₂分子拉曼光谱的调控机制（图7）。拉曼光谱作为散射光谱，与红外吸收光谱形成互补表征，能够通过分子极化率的变化反映不同振动模式的响应特性。在200–4000 cm^-1范围内，光谱特征峰依次对应以下振动模式：低频区的C-Cl键变形振动（C-Cl deform）、中频区的C=O键变形振动（C=O deform）、C-Cl键对称伸缩振动（C-Cl s-str）与反对称伸缩振动（C-Cl a-str），以及高频区的C=O键反对称伸缩振动（C=O a-str）。 

实验观测表明，随电场强度递增，各振动模式的拉曼位移呈现系统性红移趋势，且散射强度整体衰减。其中C=O键伸缩振动表现出最大红移量，证实该键对外电场具有最高响应灵敏度;C-Cl键振动模式的红移则进一步佐证了电场对分子整体电荷分布的调控作用。峰强度的普遍下降暗示分子极化率的改变削弱了振动模式的光散射效率，而红移现象直接反映了化学键的恢复力常数降低以及键能的减弱。这一趋势从振动光谱角度印证了外加电场对COCl₂分子化学活性的增强效应，为理解其在外场作用下的解离倾向提供了重要依据。 

图7.不同外加电场下拉曼光谱的变化。
Figure 7. Variations in Raman spectra under different external electric fields.

3.5外加电场对COCl₂的紫外可见光谱的影响
3.5 Influence of External Electric Field on UV-Vis Spectra of COCl₂

基于不同优化方法的对比分析，本研究采用BPV86/6-311G+（2d，p）基组进行几何优化，结合TD-SCF计算方法，系统地研究了外加电场（0~7.713V∙nm^-1）作用下COCl₂分子的紫外可见光谱特性的影响机制（图8）。在零电场的条件下，COCl₂分子于183.8 nm处呈现特征吸收峰。随着增大至7.713 V·nm⁻¹，吸收光谱发生显著展宽，同时伴随18.2 nm的红移现象，即吸收峰位置从183.8 nm逐渐偏移至188.0 nm。该光谱演化规律表明，外电场作用可有效降低分子电子跃迁的能垒，导致激发态电子结构发生显著重组。 

为进一步阐明COCl₂分子在外加电场作用下的激发能变化机制，本研究构建了前九个激发态激发能与电场强度的关联模型，并绘制了相应的变化曲线（图9）。研究结果表明，随着外加电场强度的逐步增强，各激发态的激发能整体呈递减趋势，且在临界电场强度（15.426 V·nm⁻¹）后呈现非线性加速下降特征。第一激发态的能量降低显著，受外部电场影响很大。在低激发态状态下，外部电场可显著影响其能量^[25]。该现象证实外电场可显著增强分子轨道杂化效应，降低电子激发过程的能量阈值，即分子内部电子在外加电场的影响下更易跃迁至激发态。值得注意的是，激发能曲线的改变与3.3节所述的分子解离阈值具有显著相关性，进一步验证了强电场环境下COCl₂分子稳定性降低的动力学机制。
To elucidate excitation energy variation mechanisms under external fields, we established correlation models between excitation energies of the first nine excited states and field intensity, plotting corresponding curves (Figure 9). Results show gradual decrease of excitation energies with increasing field strength, exhibiting nonlinear accelerated decline beyond critical intensity (15.426 V·nm⁻¹). The first excited state demonstrates prominent energy reduction with strong field dependence. Low-lying excited states exhibit significant energy susceptibility to external fields, confirming enhanced orbital hybridization effects and reduced energy thresholds for electronic excitation. Notably, altered excitation energy curves correlate strongly with molecular dissociation thresholds described in Section 3.3, validating COCl₂ destabilization mechanisms under strong fields.
To elucidate excitation energy variation mechanisms under external fields, we established correlation models between excitation energies of the first nine excited states and field intensity, plotting corresponding curves (Figure 9). Results show gradual decrease of excitation energies with increasing field strength, exhibiting nonlinear accelerated decline beyond critical intensity (15.426 V·nm⁻¹). The first excited state demonstrates prominent energy reduction with strong field dependence. Low-lying excited states exhibit significant energy susceptibility to external fields, confirming enhanced orbital hybridization effects and reduced energy thresholds for electronic excitation. Notably, altered excitation energy curves correlate strongly with molecular dissociation thresholds described in Section 3.3, validating COCl₂ destabilization mechanisms under strong fields.

图8 不同外加电场下紫外可见光谱的变化。
Figure 8. Variations in UV-Vis spectra under different external electric fields.

图9 COCl₂的九种激发能随电场变化对应的能量变化。
Figure 9. Energy variations corresponding to nine excitation states of COCl₂ under changing electric fields.

3.6外加电场对COCl₂分子的解离的影响
3.6 Effect of External Electric Field on COCl₂ Molecular Dissociation
3.6 Effect of External Electric Field on COCl₂ Molecular Dissociation

本研究采用BPV86杂化泛函结合6-311G+(2d,p)基组，对光气（COCl₂）分子体系进行几何优化与电子结构计算。通过构建沿C=O键轴向的外加电场模型，在键长0.7×10^-10 m至2.3×10^-10 m范围内以0.1×10^-10 m为步长进行单点能扫描，系统考察不同电场强度下分子解离能的影响机制。
Using BPV86 hybrid functional with 6-311G+(2d,p) basis set, we performed geometric optimization and electronic structure calculations for phosgene (COCl₂). By constructing an axial external field model along C=O bonds, single-point energy scanning was conducted at 0.1×10⁻¹⁰ m intervals within 0.7–2.3×10⁻¹⁰ m bond length range to systematically investigate field intensity effects on dissociation energy.
Using BPV86 hybrid functional with 6-311G+(2d,p) basis set, we performed geometric optimization and electronic structure calculations for phosgene (COCl₂). By constructing an axial external field model along C=O bonds, single-point energy scanning was conducted at 0.1×10⁻¹⁰ m intervals within 0.7–2.3×10⁻¹⁰ m bond length range to systematically investigate field intensity effects on dissociation energy.

弱电场区间(0~12.586 V·nm^-1)势能曲线呈现典型阱势特征（图10）：当键长增至约1.2×10^-10 m时，体系总能量陡降至局域极小值，随后随键长增加呈现单调递增趋势。随着电场强度从0增至12.586 V·nm^-1，势阱深度从-1033.908 Hartree降至-1033.936 Hartree，降幅达0.028 Hartree，表明电场通过调控分子轨道电子分布削弱化学键稳定性，从而促使分子解离。为了进一步探讨COCl₂分子解离能的变化趋势，我们继续增加电场强度，获得了强电场下的解离能曲线。
Weak-field region (0–12.586 V·nm⁻¹) potential energy curves show typical well characteristics (Figure 10): When bond length reaches ~1.2×10⁻¹⁰ m, system energy sharply decreases to local minima before monotonically increasing. As field intensity increases from 0 to 12.586 V·nm⁻¹, potential well depth decreases from -1033.908 Hartree to -1033.936 Hartree (0.028 Hartree reduction), indicating field-induced orbital electron redistribution weakens bond stability. Strong-field dissociation energy curves were subsequently obtained through intensified fields.
Weak-field region (0–12.586 V·nm⁻¹) potential energy curves show typical well characteristics (Figure 10): When bond length reaches ~1.2×10⁻¹⁰ m, system energy sharply decreases to local minima before monotonically increasing. As field intensity increases from 0 to 12.586 V·nm⁻¹, potential well depth decreases from -1033.908 Hartree to -1033.936 Hartree (0.028 Hartree reduction), indicating field-induced orbital electron redistribution weakens bond stability. Strong-field dissociation energy curves were subsequently obtained through intensified fields.

在强电场区间（15.426–25.713 V·nm⁻¹）势阱深度随电场强度增加呈衰减趋势（图11），当电场强度达到25.713 V·nm^-1时极小值已降至-1033.995 Hartree，证实C=O键在强电场作用下变得更加脆弱，更容易断裂，进而加速COCl₂分子的解离过程。解离势垒被定义为最低能量点与C=O键长最大时的不稳定点之间的能量差。通过解离势垒与电场强度的线性回归分析（图12），获得拟合优度R²=0.99577，表明势垒与电场强度之间呈现出良好的线性关系。因此，根据该拟合关系可以计算出，当外加电场强度达到55.347 V·nm⁻¹时，势垒趋近于零，C=O键断裂，此时COCl₂分子发生不可逆解离。该定量关系表明调控外电场的强度可有效降低COCl₂分子解离过程的活化能。
In strong-field region (15.426–25.713 V·nm⁻¹), potential well depth exhibits attenuation with increasing field intensity (Figure 11). At 25.713 V·nm⁻¹, the minimum decreases to -1033.995 Hartree, confirming C=O bond vulnerability enhancement under strong fields. Dissociation barriers (energy difference between minima and unstable points at maximal bond length) show linear correlation with field intensity (R²=0.99577 in Figure 12). Extrapolation predicts irreversible COCl₂ dissociation at 55.347 V·nm⁻¹ when barriers approach zero, demonstrating effective activation energy reduction through field modulation.
In strong-field region (15.426–25.713 V·nm⁻¹), potential well depth exhibits attenuation with increasing field intensity (Figure 11). At 25.713 V·nm⁻¹, the minimum decreases to -1033.995 Hartree, confirming C=O bond vulnerability enhancement under strong fields. Dissociation barriers (energy difference between minima and unstable points at maximal bond length) show linear correlation with field intensity (R²=0.99577 in Figure 12). Extrapolation predicts irreversible COCl₂ dissociation at 55.347 V·nm⁻¹ when barriers approach zero, demonstrating effective activation energy reduction through field modulation.

图10.弱电场下COCl₂分子中沿C=O键的单点扫描势能。
Figure 10. Single-point scanning potential energy along C=O bond in COCl₂ under weak electric fields.

（箭头方向为电场增大方向）
(Arrow direction indicates increasing electric field strength)

图11.弱电场下COCl₂分子中沿C=O键的单点扫描势能。
Figure 11. Single-point scanning potential energy along C=O bond in COCl₂ under weak electric fields.

（箭头方向为电场增大方向）
(Arrow direction indicates increasing electric field strength)

图12.外加电场作用下势垒的线性拟合曲线。
Figure 12. Linear fitting curve of dissociation barriers under external electric fields.

结论
Conclusion

本研究基于密度泛函理论（DFT），采用BPV86/6-311G+(2d,p)基组，系统揭示了外加电场（0–12.855 V·nm⁻¹）对COCl₂分子结构、电子性质、红外光谱、拉曼光谱及解离动力学的多尺度调控效应，并结合TD-SCT计算方法得到外加电场（0–7.713V∙nm^-1）对COCl₂分子的紫外可见光谱特性的影响机制。实验结果表明，外加电场显著改变了分子几何构型与电子分布，导致C=O键长增加、C-Cl键长缩短，同时偶极矩显著增大，分子总能量降低，表明电场通过极化效应削弱了C=O键的共价性并增强了C-Cl键的静电相互作用，COCl₂分子趋向于稳定状态。电子结构分析显示，电场对LUMO轨道的调控效应显著强于HOMO,HOMO-LUMO能隙E_G随电场强度增加而显著缩小，激发能阈值降低，表明电场可有效降低电子跃迁能垒，同时诱导紫外-可见光谱吸收峰发生红移，显著增强了COCl₂分子的光化学活性。
This DFT study employing BPV86/6-311G+(2d,p) systematically revealed multi-scale regulatory effects of external fields (0–12.855 V·nm⁻¹) on COCl₂ molecular structure, electronic properties, infrared/Raman spectra, and dissociation dynamics. TD-SCF calculations elucidated UV-Vis spectral responses under 0–7.713 V·nm⁻¹ fields. Results demonstrate field-induced geometric distortion and electronic redistribution: C=O bond elongation, C-Cl bond contraction, enhanced dipole moment, and total energy reduction, indicating field polarization weakens C=O covalency while strengthening C-Cl electrostatic interactions. Electronic analysis shows stronger LUMO modulation than HOMO, with HOMO-LUMO gap narrowing and excitation energy reduction, confirming reduced electronic transition barriers and UV-Vis redshift that enhances photochemical activity.
This DFT study employing BPV86/6-311G+(2d,p) systematically revealed multi-scale regulatory effects of external fields (0–12.855 V·nm⁻¹) on COCl₂ molecular structure, electronic properties, infrared/Raman spectra, and dissociation dynamics. TD-SCF calculations elucidated UV-Vis spectral responses under 0–7.713 V·nm⁻¹ fields. Results demonstrate field-induced geometric distortion and electronic redistribution: C=O bond elongation, C-Cl bond contraction, enhanced dipole moment, and total energy reduction, indicating field polarization weakens C=O covalency while strengthening C-Cl electrostatic interactions. Electronic analysis shows stronger LUMO modulation than HOMO, with HOMO-LUMO gap narrowing and excitation energy reduction, confirming reduced electronic transition barriers and UV-Vis redshift that enhances photochemical activity.

振动光谱分析进一步验证了电场对各向异性化学键的差异化调控机制：红外光谱中C-Cl键对称伸缩（C-Cl s-str）振动模式呈现红移，而C=O键反对称伸缩（C=O a-str）振动模式则发生蓝移，进一步验证了电场对键能的选择性调控。拉曼光谱中C=O反对称伸缩（C=O a-str）振动峰的红移与强度减弱现象，反映了化学键恢复力常数的降低与分子极化率的改变。紫外-可见吸收光谱的特征吸收峰发生显著展宽，同时伴随红移现象，表明外电场作用可有效降低分子电子跃迁的能垒。进一步的，激发态能量的显著降低表明，外电场可显著增强分子轨道杂化效应，降低电子激发过程的能量阈值。
Vibrational spectroscopy validates anisotropic bond-specific regulation: Infrared C-Cl symmetric stretching (C-Cl s-str) redshifts versus C=O asymmetric stretching (C=O a-str) blueshifts confirm selective bond energy modulation. Raman C=O a-str redshift and intensity reduction reflect decreased restoring force constants and altered polarizability. UV-Vis absorption broadening with redshift indicates reduced electronic transition barriers. Excited-state energy reduction confirms enhanced orbital hybridization and lowered excitation thresholds under fields.

通过构建沿C=O键轴向的外加电场模型，进行单点能扫描势能面分析表明，C=O键解离势垒随电场强度增大呈线性下降趋势。对势垒与外部电场强度进行线性回归分析，获得拟合优度R²=0.99577。根据该拟合关系可外推得，当外加电场强度达到55.347 V·nm⁻¹时，势垒趋近于零，COCl₂分子完全解离。这些发现从光谱学与动力学角度全面揭示了外加电场对COCl₂分子化学活性的增强效应，为开发电催化或等离子体辅助降解技术提供了理论依据。
Axial field model potential energy surface analysis reveals linear decrease of C=O dissociation barriers with field intensity (R²=0.99577). Extrapolation predicts complete COCl₂ dissociation at 55.347 V·nm⁻¹. These findings comprehensively elucidate field-enhanced chemical activity from spectroscopic and kinetic perspectives, providing theoretical foundations for electrocatalytic/photocatalytic degradation technologies.

引用
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