利用時域解析霍式轉換紅外光譜法研究O(1D)與氫氣之反應動態學

Abstract

吾人利用步進式時域解析霍氏紅外光光譜技術，研究O(1D)與氫氣之反應動態學。O(1D)以248 nm雷射光解O3產生，與H2反應後產生激發態的OH，觀測產物OH之振轉動放光光譜，在O(1D)+H2實驗中，可觀測到產物OH之最高振動態到v = 4 ( J′ = 14.5 )，而最高轉動躍遷能階J′ = 25.5 ( v = 1 )之放光。 利用GRAMS軟體在0.6 cm□1的解析度下用模擬光譜模擬重疊之F1、F2以及e、f奇偶性之譜線，以得到其轉動及振動態分佈，然而光譜的訊號與雜訊比不夠好造成不夠理想的誤差範圍。在實驗的誤差範圍內，各振動態的P1、P2以及e、f分支之轉動分佈沒有明顯差異，將e、f奇偶性合併之P1、P2分支有相同的分佈趨勢。e、f分支之比值受到轉動弛緩的影響不明顯，且與雷射誘發螢光法的實驗結果不一致，有待進一步探討。 將P1、P2以及e、f分支合併之各振轉動分佈與Yang等人的實驗結果以及理論計算的預測值做比較有良好的一致性，轉動分佈呈現Boltzmann分佈，所得到各振動態( v = 1-4 )的轉動溫度分別約為88600±500 K、31000±300 K、10300±400 K以及3400±200 K，平均轉動能量為38.1±2.3 kJ mol□1，觀測到產物各振動態的分佈為( v = 1 )：( v = 2 )：( v = 3 )：( v = 4 ) = 1：0.81：0.7：0.41，平均振動溫度約為28800±300 K，平均振動能量為27.4±3.5 kJ mol□1。

The OH radical is known to play an important role in the atmosphere. It is formed by reactions of O atoms with H-containing molecules. The O(1D) + H2 reaction, the simplest yet one of the most fundamental reactions, has been extensively studied by many research groups using various techniques. Typically the sensitive laser-induced fluorescence (LIF) technique is employed for detection of OH. However, because of predissociation of OH at higher rotational and vibrational levels, detection of OH in these states are difficult. Although Rydberg tagging technique1 provides detailed information on the vibrational-rotational distribution of OH product, F1/ F2 and e/f components but except for v= 4 of OH were unresolved. We employed a step-scan Fourier-transform IR spectrometer to observe emission spectrum of OH emission (v = 1-4) produced from the reaction O(1D) + p-H2 in the spectra region 2300-3900 cm-1. O(1D) was produced by photolysis of O3 with light from a KrF excimer laser at 248 nm. Upon irradiation of a flowing mixture of O3 (38 mTorr) and p-H2 (76 mTorr) at 248 nm, emission of OH from highly internally excited states appeared within 2 μs, followed by rapid relaxation. The preliminary data at resolution of 0.6 cm-1, we were able to resolve most spectral line and derive population for each of the e/f and F1/F2 component. A small preference of the e/f propensity indicates that the reaction intermediate is short-lived.