Study of CO_2 laser pumped infrared emission spectroscopy

发射光谱法的灵敏度通常高于吸收光谱法。然而，在红外区，由于发射方法的波长比可见光和紫外区长，其应用受到限制，主要是双原子分子。另一方面，高功率CO_2激光器是产生远红外激光振荡的良好泵浦源，其中CO_2激光器泵浦的分子必须在10 μ m范围内具有合适的振动频率。本研究以SF_6分子为敏化剂，利用SF_6分子吸收CO_2激光能量，热SF_6分子将吸收的能量传递给其它分子，观察分子的红外或远红外辐射。通过高分辨率傅里叶变换光谱仪观察发射。CO、N_2O、C_2H_2、CH_4、过氧化二叔丁基等具有非零振动跃迁矩的分子均表现出较强的发光。对其中N_2O分子的发射光谱进行了详细的分析，并根据振转谱线的相对强度确定了其转动激发温度为819（9）K。N_2O分子的振动、旋转和平移运动的总能量达到7000 cm ~ 2以上<-1>，说明CO_2激光至少有8个光子的能量转移到N_2O分子上。结果表明，该方法对能量传递过程的研究是有用的。

Sensitivity of emission spectroscopy is generally higher than that of absorption spectroscopy. However, in infrared region the emission method has disadvantage because of longer wavelength compared with the cases in visible and ultraviolet regions, and its application is limited mainly diatomic molecules. On the other hand, a high-power CO_2 laser is known to be a good pumping source for generating far-infrared laser oscillation, where molecules pumped by CO_2 laser must have suitable vibrational frequencies in the 10 mum region. Therefore, all molecules do not necessarily give infrared or far-infrared emission.In the present study, the SF_6 molecule has been used as sensitizer for observing emission from molecules, where SF_6 absorbs CO_2 laser energy, and the hot SF_6 molecules transfer the absorbed energy to other molecules. The emission was observed by a high-resolution Fourier transform spectrometer. All molecules with non-zero vibrational transition moments like as CO,N_2O,C_2H_2, CH_4, di-tert butyl peroxide etc. showed strong emission. Among these molecules, N_2O emission spectra were analyzed in detail, and rotational excitation temperature of 819 (9) K was determined from the relative intensities of vibration-rotation lines. The total energy of vibration, rotation and translation motions of N_2O reached up to more than 7000 cm^<-1>, which indicates that at least 8 photon energy of the CO_2 laser is transfered to the N_2O molecule. It is found that the present method is useful for study of energy transfer process.