Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/10750

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Title: | ASPECTS OF LINE STRENGTHS AND HALF WIDTHS FOR SOME OF THE $\nu_{2}$ BAND LINES OF $^{12}C^{16}O_{2}$ |

Creators: | Rinsland, C. P.; Devi, V. Malathy; Das, Palash P.; Rao, K. Narahari; Fridovich, B. |

Issue Date: | 1979 |

Publisher: | Ohio State University |

Abstract: | The objective of this paper is to describe briefly a few practical problems that came about during the determination of line strengths from infrared spectra. The spectral data obtainable with a diode laser at Doppler-limited spectral resolution do indeed provide good experimental data for obtaining the strengths of infrared spectral lines. However, it may be important to realize that the effects of mode mixing may be quite significant and at times may give rise to subtle unexpected situations. A few examples will be given to clarify these effects in terms of the diode laser spectra obtained in the $nU$2 band of $^{12}C^{16}O_{2}$ at 15$\mu$m. Several R branch lines in this band have been studied and it was noticed that, for certain J values, maximum absorption and/or integrated absorptions did not follow a regular pattern when compared with neighboring R(J) lines although in all cases, the reproducibility of data has been excellent. By scanning over larger spectral intervals than were needed for recording the scan for a line to get a strength measurement some, of these anomalies could be traced to mode mixing. The careful monitoring of the simultaneously recorded fringe system from a Fabry-Perot etalon may give one indication of this mode mixing. It would of course help if two different diodes can be used for the same measurements. A method has been found practicable in determining the distortion of Doppler-lines caused by a Gaussian instrument function. In this method, the absorbtance A(nU) is expanded in a series and convoluted with a normalized Gaussian instrument function. If the Doppler half width at half height (HWHH) is $b_{D}$, and the instrument HWHH is d, we define $\beta = {^{b}} D/(\ell n2)^{\frac{1}{2}}$ and $5= d/(\ell n2)^{\frac{1}{2}}$. The convolution can be performed in a closed form and results in a series. \[ A^{\prime}(\nu)=\sum_{n=1}^{\infty}(-1)^{(n-1)}\frac{c^{n}}{n:n^{\frac{1}{a}}}\left[\frac{1}{n} +(8/\beta)^{2}\right]^{-\frac{1}{8}}. Exp. \frac{-\nu^{2}}{\beta^{2}[(1/n)+(\delta /\beta)^{2}]} \] Term by term integration of bath $A(\nu)$ and $A^{\prime}(\nu)$ to find the total integrated absorption results in the well known series expression of Ladenburg (Z. Physik 65, 200 (1930)). This method has been used to produce charts of $A^{\prime}(0)$ ie. $A^{\prime}$(at line center) versus convoluted absorption for various values of $b_{D}$ and d. The charts allow us to find d for a measured $A^{\prime}(0)$. |

Description: | Author Institution: |

URI: | http://hdl.handle.net/1811/10750 |

Other Identifiers: | 1979-FA-06 |

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