利用間質隔離法研究3-羥基(1氫)吡啶鹽陽離子及 3-羥基(1氫)吡啶鹽基在para-H2間質中之紅外光譜

Abstract

此研究利用低溫間質隔離技術搭配霍氏轉換紅外光譜儀(FTIR)研究3-羥基吡啶鹽陽離子及3-羥基吡啶鹽基在para-H2(p-H2)間質中之紅外光譜。混合p-H2與極少量3-羥基吡啶並沉積於3.2 K靶面之同時，以電子束撞擊樣品間質，產生3-羥基(1氫)吡啶鹽陽離子及3-羥基(1氫)吡啶鹽基。將電子撞擊後之樣品間質放置在黑暗中20小時後，可觀察到位於 3594.4、3380.0、3127.2、3115.6、3084.3、1610.6、1587.4、1562.1、1483.4、1331.5、1319.4、1266.1、1193.8、1167.5、1107.8、1042.3、925.8、831.5、780.4以及665.2 cm-1之3-羥基(1氫)吡啶鹽陽離子吸收譜線強度下降；而位於3646.2、3493.4、3488.7、3067.3、1546.7、1465.4、1425.8、1349.6、1295.9、1244.1、1209.1、1177.3、1090.5、1038.3、979.8、818.0、685.2、573.8以及503.1 cm-1之3-羥基(1氫)吡啶鹽基吸收譜線強度上升，且以520 nm光解後吸收強度下降，並在450 nm照射後譜線明顯消失。 3-羥基(1氫)吡啶鹽陽離子及3-羥基(1氫)吡啶鹽基振動模吸收譜線之指派係由比較實驗光譜與B3LYP/aug-cc-pVTZ理論計算預測之非簡諧振動波數及吸收強度所得到。而在理論計算中3-羥基(1氫)吡啶鹽陽離子及3-羥基(1氫)吡啶鹽基皆為最穩定之異構物，與實驗之結果一致。

The IR absorption spectra of the 3‑hydroxy-(1H)-pyridinium (C5H5NOH+) cation and 3-hydroxy-(1H)-pyridinyl (C5H5NOH) radical produced on electron bombardment during matrix deposition of a mixture of 3‑hydroxypyridine (C5H5NO) and p-H2 at 3.2 K were recorded. The IR absorption lines at 3594.4, 3380.0, 3127.2, 3115.6, 3084.3, 1610.6, 1587.4, 1562.1, 1483.4, 1331.5, 1319.4, 1266.1, 1193.8, 1167.5, 1107.8, 1042.3, 925.8, 831.5, 780.4 and 665.2 cm-1decreased in intensity after the matrix was maintained in darkness for 20 h, whereas lines at 3646.2, 3493.4, 3488.7, 3067.3, 1546.7, 1465.4, 1425.8, 1349.6, 1295.9, 1244.1, 1209.1, 1177.3, 1090.5, 1038.3, 979.8, 818.0, 685.2, 573.8 and 503.1 cm-1 increased. The lines which decreased in intensity were assigned to 3‑hydroxy-(1H)-pyridinium cation, and which increased in intensity were assigned to 3-hydroxy-(1H)-pyridinyl radical. The intensities of lines of 3-hydroxy-(1H)-pyridinyl radical decreased upon irradiation at 520 nm and decreased significantly upon irradiation at 450 nm. Observed wavenumbers and relative intensities of these species agree satisfactorily with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3LYP/aug-cc-pVTZ method. The formation of 3‑hydroxy-(1H)-pyridinium cation and 3-hydroxy-(1H)-pyridinyl radical is consistent with theoretical predictions indicating that they are the most stable among all isomers.