Study of CO_2 laser pumped infrared emission spectroscopy

发射光谱的灵敏度一般高于吸收光谱。但在红外波段，由于发射波长较长，在可见光和紫外区的发射波长较长，其应用受到限制，主要是双原子分子。另一方面，高功率的CO_2激光器被认为是产生远红外激光振荡的良好泵浦源，其中被CO_2激光泵浦的分子必须在10微米范围内具有合适的振动频率。因此，并不是所有的分子都会发出红外或远红外辐射。在本研究中，SF_6分子被用作观察分子发射的增感剂，其中SF_6吸收CO_2激光能量，热的SF_6分子将吸收的能量传递给其他分子。用高分辨率傅里叶变换光谱仪观测到了发射。所有具有非零振动跃迁矩的分子，如CO、N_2O、C_2H_2、CH_4、二叔丁基过氧化氢等都有很强的发射。在这些分子中，详细分析了N_2O发射光谱，并根据振动-旋转线的相对强度确定了819(9)K的转动激发温度。N_2O分子的振动、旋转和平移运动总能量达到7000 cm~(-1)~(-1)以上，表明至少有8个光子能量被转移到N_2O分子中。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.