Saturation spectroscopy of R(0), R(2) and P(2) lines in the (2-0) band of HD
Frank M. J. Cozijn, Meissa L. Diouf, W. Ubachs
Abstract
Abstract Lamb-dips of R(0), R(2) and P(2) rovibrational transitions in the (2-0) overtone band of the HD molecule are measured at cryogenic temperatures using the technique of NICE-OHMS spectroscopy. Resulting transition frequencies are $$214\,905\,335\,240\,(100)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>214</mml:mn> <mml:mspace/> <mml:mn>905</mml:mn> <mml:mspace/> <mml:mn>335</mml:mn> <mml:mspace/> <mml:mn>240</mml:mn> <mml:mspace/> <mml:mo>(</mml:mo> <mml:mn>100</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> kHz for R(0), $$219\,042\,856\,794\,(150)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>219</mml:mn> <mml:mspace/> <mml:mn>042</mml:mn> <mml:mspace/> <mml:mn>856</mml:mn> <mml:mspace/> <mml:mn>794</mml:mn> <mml:mspace/> <mml:mo>(</mml:mo> <mml:mn>150</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> kHz for R(2) and $$206 \,898 \,802\,150 \,(150)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>206</mml:mn> <mml:mspace/> <mml:mn>898</mml:mn> <mml:mspace/> <mml:mn>802</mml:mn> <mml:mspace/> <mml:mn>150</mml:mn> <mml:mspace/> <mml:mo>(</mml:mo> <mml:mn>150</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> kHz for P(2). Small, but systematic deviations (at 1.7 $$\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>σ</mml:mi> </mml:math> level) are found from advanced ab initio calculations, supporting results from previous studies probing other lines in the (2-0) band. From a combination difference between the R(0) and P(2) lines, an accurate value for rotational-level spacing in the $$v=0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>v</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:math> ground state is determined, of $$\Delta _{(J=2)-(J=0)}= 8\,006\,533\,168\,(26)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>Δ</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>J</mml:mi> <mml:mo>=</mml:mo> <mml:mn>2</mml:mn> <mml:mo>)</mml:mo> <mml:mo>-</mml:mo> <mml:mo>(</mml:mo> <mml:mi>J</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>8</mml:mn> <mml:mspace/> <mml:mn>006</mml:mn> <mml:mspace/> <mml:mn>533</mml:mn> <mml:mspace/> <mml:mn>168</mml:mn> <mml:mspace/> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>26</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> kHz, well in agreement with theory (at 0.6 $$\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>σ</mml:mi> </mml:math> ). Based on the observation of the dispersive line shape of R(0), the status of proposed models for the elusive line shapes of saturated transitions in HD is discussed.