碘穩頻系統常用來當作雷射光頻率標準。我們測量了127I2 P(28) (24-0) 譜線的絕對頻率。碘分子與鋰離子的躍遷頻率差了數個GHz，因此碘分子的頻率測量可以用來當作鋰離子光譜的頻率標準。在此實驗中，我們用1097 nm的外腔式雷射(external-cavity diode laser) 和一個倍頻系統來產生548.5 nm的雷射光，並且用調製傳遞光譜法 (modulation transfer spectroscopy) 來得到碘分子光譜。我們在碘分子蒸氣壓在7.8 Pa時測量a1, a10和a15譜線。我們測量了碘蒸氣壓對躍遷頻率的影響，並用此8.9(1.2) kHz/Pa修正得到絕對躍遷頻率。最後a1, a10, a15 譜線頻率為546437908826(12) kHz, 546438483384(12) kHz以及 546438771985(12) kHz。實驗結果與IodineSpec5的計算值相符合。我們也有探討氣壓與雷射功率對線寬的影響。在未來的研究中，我們將會測量其他的540 nm到550 nm範圍的碘分子躍遷譜線，其中有一些譜線將可以當作鋰離子光譜實驗的參考頻率。

The iodine stabilization system is usually used as an optical frequency standard. We report the absolute frequency measurement of 127I2 P(28) (24-0) lines. The frequency of iodine transitions is several GHz away from the Li+ ion transition and can be used as reference for lithium ion spectroscopy. In this experiment, we use 1097 nm external-cavity diode laser and a double system to produce 548.5 nm light, and use modulation transfer spectroscopy to obtain the iodine spectrum. We measure a1, a10, a15 lines, and they are measured at a vapor pressure of 7.8 Pa. As a result, we correct them by the pressure shift which is measured to be 8.9(1.2) kHz/Pa. The final results of the a1, a10, a15 are 546437908826(12) kHz, 546438483384(12) kHz, and 546438771985(12) kHz respectively. The results agree with the calculated values of IondineSpec5. The effect of pressure and power broadening are also investigated. For the future work, we will measure other transitions of molecular iodine between 540-550 nm, and some of them can also be used as references for lithium ion spectroscopy.

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