Mondelain D, de Casson L Boux, Fleurbaey H, Kassi S, Campargue A
Univ. Grenoble Alpes, CNRS, LIPhy, Bat. E, 140 rue de la Physique, 38400 Saint-Martin d'Hères, France.
Phys Chem Chem Phys. 2023 Aug 30;25(34):22662-22668. doi: 10.1039/d3cp03187j.
A series of spectra of the quadrupolar electric S(2) transition of H in the 1-0 band near 4917 cm has been recorded at seven pressure values between 2 and 100 Torr. The comb-referenced cavity ring down spectroscopy (CR-CRDS) technique was used for the recording of this very weak transition. The accuracy of the spectrum frequency axis is achieved by linking the CRDS setup to an optical frequency comb referenced to a GPS-referenced 10 MHz rubidium clock. Applying a multi-spectrum fit procedure to the seven averaged spectra with a quadratic speed dependence Nelkin-Ghatak profile, the transition frequency is determined ( = 147 408 142 357 kHz) with an uncertainty of 150 kHz (∼1 × 10 in relative). This represents the smallest uncertainty achieved so far for a transition in the fundamental band of H. The experimental frequency reported in this work is 1.53 MHz higher than the best-to-date theoretical value. This difference represents 1.5 times the 1-uncertainty (about 1 MHz) of the calculated frequency. The measurements also allow for the determination of the absolute intensity value of the S(2) line which shows an agreement with the value at the per mil level. In addition, the cross section of the collision induced absorption (CIA) underlying the S(2) line is accurately retrieved from the quadratic pressure dependence of the baseline level of the recorded spectra.
在4917厘米附近的1-0波段，已在2至100托的七个压力值下记录了一系列氢的四极电S(2)跃迁光谱。采用梳状参考腔衰荡光谱（CR-CRDS）技术来记录这一极其微弱的跃迁。通过将CRDS装置与一个参考GPS参考10兆赫铷钟的光学频率梳相连，实现了光谱频率轴的高精度。对具有二次速度依赖Nelkin-Ghatak轮廓的七个平均光谱应用多光谱拟合程序，确定跃迁频率为（= 147408142357千赫），不确定度为150千赫（相对不确定度约为1×10）。这是迄今为止氢基频带跃迁所达到的最小不确定度。本工作中报告的实验频率比目前最好的理论值高1.53兆赫。这一差异是计算频率1不确定度（约1兆赫）的1.5倍。这些测量还能确定S(2)线的绝对强度值，该值与千分位水平的 值相符。此外，从记录光谱基线水平的二次压力依赖性中准确提取了S(2)线下方碰撞诱导吸收（CIA）的截面。
