• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Solid State Communications >An infrared spectroscopic study of NH4Br-ammonium bromide to 55 GPa
【24h】

An infrared spectroscopic study of NH4Br-ammonium bromide to 55 GPa

机译：NH4Br-溴化铵至55 GPa的红外光谱研究

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

We have measured the infrared spectrum of NH4Br-ammonium bromide to 55 GPa at 300 K. The hydrogen bond in this system is initially nearly linear, and the magnitude of volumetric compression over this pressure range is between 45% and 55%: thus, dramatic compression of the N-(HBr)-Br-... distances is expected. However, we observe pressure shifts of the internal modes of the ammonium ion that are small, non-linear and change in sign under compression. For example, the v(3)-asymmetric stretching band of the NH4 group near 3145 cm(-1) undergoes an initial decrease with pressure to similar to 5 GPa, followed by near-constancy to 20 GPa, and increases in frequency at higher pressures: it has essentially an identical frequency at 30 GPa as it does at 2.5 GPa. The pressure dependences of the internal modes indicate that if strong hydrogen bonding is present in the system, or is induced by pressure, then there must be competing and compensating effects that produce near-constancy or pressure-induced increases of the internal ammonium ion stretching frequencies as well as decreases in the internal bending frequencies. Our results indicate that three effects likely prohibit the pressure-induced onset of strong hydrogen bonding within the system: (1) a change in the N-H...Br bond angle at high pressures, (2) overbonding on the bromine ion by the surrounding hydrogen atoms, and (3) inter-ammonium ion hydrogen-hydrogen repulsion which is enhanced with increasing pressure and decreasing volume. Systematics of the pressure dependences of the N-H stretching frequencies of the ammonium halides indicate that the last effect, H-H repulsion, dominates in these systems. Thus, it is the abundance of hydrogen within the NH4Br lattice that produces the primary effect on the pressure shift of the N-H stretching vibrations, rather than increased hydrogen bonding. (c) 2006 Elsevier Ltd. All rights reserved.
机译：我们在300 K下测量了NH4Br-溴化铵至55 GPa的红外光谱。该系统中的氢键最初几乎是线性的，在此压力范围内，体积压缩的幅度介于45％和55％之间： N-（HBr）-Br -...距离的压缩是可以预期的。但是，我们观察到铵离子内部模式的压力变化很小，呈非线性并且在压缩下符号改变。例如，NH4基团在3145 cm（-1）附近的v（3）不对称拉伸带经历了初始降低，压力接近5 GPa，随后接近恒定，达到20 GPa，并在更高的频率下增加了频率压力：它在30 GPa时的频率与2.5 GPa时的频率基本相同。内部模式对压力的依赖性表明，如果系统中存在强氢键或由压力引起，则必须存在竞争性和补偿性作用，使内部铵离子拉伸频率接近恒定或因压力而增加以及减少内部弯曲频率。我们的结果表明，三种作用可能会阻止压力诱导的系统内强氢键的发生：（1）高压下NH ... Br键角的变化；（2）周围环境对溴离子的过度键合氢原子，和（3）铵间离子氢氢排斥力，随着压力的增加和体积的减小而增强。卤化铵的N-H拉伸频率的压力依赖性的系统分析表明，在这些系统中，最后的作用H-H排斥作用占主导地位。因此，正是NH4Br晶格中的大量氢对N-H拉伸振动的压力位移产生了主要影响，而不是增加了氢键。 （c）2006 Elsevier Ltd.保留所有权利。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号