浓度微扰下硝酸水溶液中氢键作用的二维相关拉曼光谱研究

doi:10.3964/j.issn.1000-0593(2025)04-0958-06

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摘要：硝酸被称为“国防工业之母”，其水溶液的稀释浓度对火炸药生产至关重要。通过搭建腔增强型拉曼光谱仪，提高拉曼激发和收集效率，实现对硝酸质量分数（ω）为35.49%～88.98%的细微浓度差异的硝酸水溶液进行测量。分析900～1 400 cm^-1范围内的硝酸拉曼光谱，发现965 cm^-1处N—OH伸缩振动模式随着硝酸浓度变化发生显著频移。随着硝酸质量分数增加，当35.49%≤ω≤55.10%时，N—OH伸缩振动模式快速红移，这归因于HNO₃—nH₂O（n=1, 2, …）团簇结构的形成；当ω>55.10%时，N—OH伸缩振动模式红移程度逐渐变小，这可能是因为硝酸与水分子之间形成的氢键逐渐减少的缘故；当ω>68.78%时，N—OH伸缩振动模式红移程度增大，这源于硝酸分子内氢键的增多。此外，深入研究1 050 cm^-1处N—O全对称伸缩振动模式与1 300 cm^-1处N—OH反对称伸缩振动模式的谱峰强度随硝酸浓度的变化。随着硝酸质量分数增加，当35.49%≤ω≤55.10%时，1 050与1 300 cm^-1的拉曼峰面积比快速减小；当ω>55.10%时，该拉曼峰面积比减小幅度放缓；当ω>68.78%时，该拉曼峰面积比的变化趋于稳定。1 050与1 300 cm^-1的拉曼峰面积比值的减小可以归因于 NO^-₃（N—O全对称伸缩振动模式）逐渐减少，而未解离HNO₃（N—OH反对称伸缩振动模式）逐渐增加。上述光谱峰频移和强度变化表明，在可用样本量范围内，当ω分别达到55.10%和68.78%时，HNO₃—nH₂O团簇结构均会发生转变。结合密度泛函理论（DFT）进一步阐释谱峰强度和频移变化机理。当35.49%≤ω≤55.10%时，硝酸水溶液中HNO₃—3H₂O和HNO₃—2H₂O是主要存在形式。当ω>55.10%时，溶液中HNO₃—nH₂O逐渐转变为HNO₃—H₂O团簇。当ω>68.78%时，硝酸水溶液中未解离的HNO₃逐渐占据优势。最后，对一维拉曼光谱进行二维相关分析，揭示HNO₃/NO^-₃的谱峰来源。结果证实1 308和958 cm^-1的谱峰代表未解离的HNO₃分子，1 051 cm^-1处谱峰属于解离 NO⁺₃。这些结果有助于深入理解不同浓度硝酸水溶液中分子间相互作用变化，为硝酸在化工、材料化学以及国防工业领域的应用提供参考。

关键词：拉曼光谱；硝酸水溶液；氢键作用；二维相关光谱；DFT计算

Abstract：Nitric acid is known as the “mother of the national defense industry”, and the dilution concentration of its aqueous solution is crucial for producing explosives. This paper improves the Raman excitation and collection efficiency by constructing a cavity-enhanced Raman spectrometer. It achieves the measurement of aqueous nitric acid solutions with fine concentration differences ranging from 35.49% to 88.98% in nitric acid mass fraction (ω). Analyzing the Raman spectra of nitric acid within the range of 900～1 400 cm^-1, it was found that the N—OH stretching vibration mode at 965 cm^-1 showed a significant frequency shift with changes in nitric acid concentration. When 35.49%≤ω≤55.10%, an increase in nitric acid concentration induces a rapid red shift in the N—OH stretching vibration mode, attributed to the formation of HNO₃—nH₂O (n=1, 2, …) cluster structures. When ω>55.10%, the degree of redshift in the N—OH stretching vibration mode gradually decreases, which may be because the hydrogen bonds (H-bonds) formed between nitric acid and water molecules decrease. When ω>68.78%, the degree of redshift in the N—OH stretching vibration mode expands again due to increased H-bonds within nitric acid molecules. In addition, the intensity of the N—O fully symmetric stretching vibration mode at 1 050 cm^-1 and the N—OH asymmetric stretching vibration mode at 1 300 cm^-1 as a function of nitric acid concentration were also studied. When 35.49%≤ω≤55.10%, the area ratio of Raman peaks at 1 050 and 1 300 cm^-1 decreases rapidly as the nitric acid concentration increases. However, the decrease in the area ratio at 1 050 and 1 300 cm^-1 slows down atω>55.10%. The area ratio tends to stabilize at ω>68.78%, which is attributed to NO^-₃ gradually decreases and undissociated HNO₃ increases. The above Raman shift and peak intensity indicate that within the available sample range in this paper, the HNO₃—nH₂O cluster structure will transform when ω reaches 55.10% and 68.78%, respectively. Further, explain the mechanism of peak intensity and frequency shift changes by combining density functional theory (DFT). The HNO₃—3H₂O and HNO₃—2H₂O cluster structures are the main forms in aqueous nitric acid solutions at 35.49%≤ω≤55.10%, and these cluster structures gradually transform into HNO₃—H₂O at ω>55.10%, and the undissociated HNO₃ gradually dominates in aqueous nitric acid solution at ω>68.78%. Finally, a two-dimensional correlation analysis was performed on the one-dimensional Raman spectrum to reveal the peak sources of HNO₃/NO^-₃. The results confirmed that the Raman peak at 1 051 cm^-1 represents NO^-₃, while the Raman peaks at 1 308 and 958 cm^-1 belong to the undissociated HNO₃ molecule. These results contribute to understanding intermolecular interactions in aqueous nitric acid solutions with different concentrations and provide a reference for the application of nitric acid in chemical engineering, material chemistry, and the national defense industry.

Key words：Raman spectroscopy; Aqueous nitric acid solution; Hydrogen bonding; Two-dimensional correlation spectroscopy; DFT calculations

收稿日期: 2024-05-20 修订日期: 2024-09-05

中图分类号:

O561.3

通讯作者: 王小卓 E-mail: xiaozhuowang77@163.com

作者简介: 杨博，1994年生，西安机电信息技术研究所助理研究员 e-mail: boyang2306@163.com

引用本文:

杨博，张雅茹，程碧瑶，李雨蔚，屈鹏飞，唐辉，柳海斌，王小卓. 浓度微扰下硝酸水溶液中氢键作用的二维相关拉曼光谱研究[J]. 光谱学与光谱分析, 2025, 45(04): 958-963.
YANG Bo, ZHANG Ya-ru, CHENG Bi-yao, LI Yu-wei, QU Peng-fei, TANG Hui, LIU Hai-bin, WANG Xiao-zhuo. Investigation of Hydrogen Bonding in Aqueous Nitric Acid Solution Under Concentration Perturbation by Two-Dimensional Correlated Raman Spectroscopy. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2025, 45(04): 958-963.

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