Revisiting Isotope Effects in Infrared Spectra of H2O, HDO and D2O

IF 2.9 3区 教育学 Q2 CHEMISTRY, MULTIDISCIPLINARY
Suleyman Ince,  and , Sefik Suzer*, 
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Abstract

Isotope effects are widely used in infrared analyses of a range of chemical systems. Water molecules with three active modes are one of the most studied for testing the applicability of theoretical models. Whereas the IR spectrum of free gaseous water is very complex due to the accompanying rotational spectral features, the ATR-FTIR spectrum of a semidry solid LiCO4 sample reveals well-resolved 3 vibrational features of seemingly isolated molecules trapped within the solid matrix. Exposure of that sample to additional H2O vapors causes an increase in the intensity of these features, while further exposure causes them to broaden, red-shift, and intensify due to formation of H-bonding-networked water aggregates. Exposure of a different sample to D2O vapors enables the recording of new and well-resolved peaks assignable to the normal vibrational modes of HDO and D2O molecules. The position and relative intensity of these peaks can be used for testing theoretical predictions, based on coupled-oscillators model, together with the approach of force constants and geometrical factors of a bent triatomic molecule. By using the ratio of the experimentally determined positions of the antisymmetric and symmetric stretching peaks of H2O, and computing the ratio of geometric factors, one can estimate ratio of the force constants within the solid and extend it to estimate the same for D2O molecule to compare with experimental data. Extracting force constant variations is a very crucial step for tracing the chemical nature of intermolecular interactions within various systems and materials. Through repeating these simple measurements, one would not only gain a deeper understanding of several advanced concepts in IR spectroscopy and isotope effects but also learn how to simplify difficult mathematical procedures. Simple measurements outlined herein would also enable visualization of gas phase H/D exchange in real-time.

Abstract Image

重述H2O、HDO和D2O红外光谱中的同位素效应
同位素效应广泛应用于一系列化学系统的红外分析。具有三种活性模式的水分子是检验理论模型适用性研究最多的分子之一。由于伴随的旋转光谱特征,自由气态水的红外光谱非常复杂,而半干燥固体LiCO4样品的ATR-FTIR光谱显示了固体基质中看似孤立的分子的良好分辨振动特征。将样品暴露在额外的H2O蒸汽中会导致这些特征的强度增加,而进一步暴露会导致它们变宽、红移,并由于形成氢键网络水聚集体而增强。将不同的样品暴露于D2O蒸汽中,可以记录新的和良好分辨的峰,这些峰可分配给HDO和D2O分子的正常振动模式。这些峰的位置和相对强度可用于验证基于耦合振子模型的理论预测,以及弯曲三原子分子的力常数和几何因子的方法。利用实验确定的H2O的不对称和对称拉伸峰位置之比,计算几何因子之比,可以估计固体内部力常数之比,并将其推广到D2O分子的力常数之比,与实验数据进行比较。提取力常数变化是追踪各种系统和材料中分子间相互作用的化学性质的一个非常关键的步骤。通过重复这些简单的测量,人们不仅可以更深入地了解红外光谱和同位素效应的几个先进概念,而且还可以学习如何简化困难的数学程序。本文概述的简单测量也可以实现气相H/D交换的实时可视化。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Chemical Education
Journal of Chemical Education 化学-化学综合
CiteScore
5.60
自引率
50.00%
发文量
465
审稿时长
6.5 months
期刊介绍: The Journal of Chemical Education is the official journal of the Division of Chemical Education of the American Chemical Society, co-published with the American Chemical Society Publications Division. Launched in 1924, the Journal of Chemical Education is the world’s premier chemical education journal. The Journal publishes peer-reviewed articles and related information as a resource to those in the field of chemical education and to those institutions that serve them. JCE typically addresses chemical content, activities, laboratory experiments, instructional methods, and pedagogies. The Journal serves as a means of communication among people across the world who are interested in the teaching and learning of chemistry. This includes instructors of chemistry from middle school through graduate school, professional staff who support these teaching activities, as well as some scientists in commerce, industry, and government.
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