Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA.
J Phys Chem A. 2012 Sep 20;116(37):9287-94. doi: 10.1021/jp3072298. Epub 2012 Sep 11.
Pulsed discharges containing methanol or ethanol produce ions having the nominal formula C,H(3),O, i.e. m/z = 31. Similar ions resulting from electron impact ionization in mass spectrometers are long recognized to have either the CH(2)OH(+) protonated formaldehyde or CH(3)O(+) methoxy cation structures. The H(2)OCH(+) oxonio-methylene structure has also been suggested by computational chemistry. To investigate these structures, ions are expanded in a supersonic beam, mass-selected in a time-of-flight spectrometer, and studied with infrared laser photodissociation spectroscopy. Sharp bands in the O-H and C-H stretching and fingerprint regions are compared to computational predictions for the three isomeric structures and their vibrational spectra. Protonated formaldehyde is the most abundant isomer, but methoxy is also formed with significant abundance. The branching ratio of these two ion species varies with precursors and formation conditions.
含有甲醇或乙醇的脉冲放电会产生具有标称式 C,H(3),O的离子，即 m/z = 31。在质谱仪中通过电子碰撞电离产生的类似离子，长期以来一直被认为具有 CH(2)OH(+)质子化甲醛或 CH(3)O(+)甲氧基阳离子结构。计算化学也提出了 H(2)OCH(+)氧鎓亚甲基结构。为了研究这些结构，离子在超音速射流中扩展，在飞行时间光谱仪中进行质量选择，并通过红外激光光解光谱进行研究。O-H 和 C-H 伸缩和指纹区域的尖锐谱带与三种异构体及其振动光谱的计算预测进行了比较。质子化甲醛是最丰富的异构体，但甲氧基也以显著的丰度形成。这两种离子物种的分支比随前体和形成条件而变化。
