利用間質隔離法研究GeNNO之紅外光譜

Abstract

吾人利用低溫間質隔離技術搭配霍氏轉換紅外光譜儀（FTIR）以紅外光譜法研究鍺原子（Ge）與氧化亞氮（N2O）在Ar間質中之反應機制。共同沉積Ge與N2O/Ar於11 K的樣品靶面上，吾人觀測到位於1443.7、1102.4及784.0 cm-1之主要較強的三根新吸收峰譜線；其餘較弱的吸收峰分別位於2859.2、1238.1/1239.7/1241.8、1255.5/1259.3及1486.4/1488.9 cm-1。 密度泛函理論（B3LYP /aug-cc-pVTZ）計算結果顯示Ge與N2O反應可能生成五種穩定結構：GeNNO、cyc-1Ge-(NN(O))、cyc-3Ge-(NNO)、GeONN、1GeNON。根據不同波長光波照射間質，其新吸收譜線消長不同，吾人可將實驗觀測之新吸收峰分組，並配合理論計算結果指派(A)位於1443.7、1102.4、784.0 cm-1之較強吸收峰為1GeNNO之nu1、nu2、nu3；位於2859.2、1238.1/1239.7/ 1241.8之較弱吸收峰為1GeNNO之2nu1及nu3 + nu4；(B)位於1255.5/1259.3 cm-1之弱吸收峰為3GeONN的nu2振動模；(C)位於1486.4/1488.9 cm-1之極弱吸收峰為cyc-1Ge-(NN(O))的nu1振動模。實驗觀測之振動波數、相對紅外光譜線強度、15N-同位素比例皆與理論計算的結果相符。 Ge與N2O 反應生成3GeNNO後，經由系統間轉換（ISC）緩弛至更穩定的 1GeNNO為反應的主要途徑，1GeNNO經193 nm、248 nm之雷射光波及波長長於525 nm (中壓汞燈加濾光片)之光波光解皆生成GeO。

Co-deposition of thermally generated atomic germanium vapor and nitrous oxide (N2O) in Ar onto a substrate at 11 K produced infrared absorption lines in several sets. The most prominent comprises intense lines at 1443.7, 1102.4, and 784.0 cm-1 that become diminished upon irradiation with UV or visible light. These lines are attributed to nu1(NO stretching), nu2 (NN + GeN stretching), and nu3 (NNO bending + NN stretching) modes of singlet GeNNO. Two additional weak features at 1238.1 and 2859.2 cm-1 are assigned as nu3 + nu4 and 2nu1 of GeNNO, respectively. Weak doublet features at 1259.3/1255.5 and 1488.9/1486.4 cm-1 are tentatively assigned to nu2 of triplet GeONN and nu1 of singlet cyc-Ge-(NN(O)), respectively. Quantum-chemical calculations on the Ge + N2O system with density-functional theory (B3LYP/aug-cc-pVTZ) predict five stable structures: GeNNO (singlet and triplet), singlet cyc-Ge-(NN(O)), triplet cyc-Ge-(NNO), GeONN (singlet and triplet), and singlet GeNON. Vibrational wavenumbers, relative IR intensities, and 15N-isotopic ratios for observed species are consistent with those computed. Irradiation of singlet GeNNO with different wavelength (248 or 193 nm, or > 525 nm) yields GeO.