zhao_2026
=========

Z\.\-F\. Zhao, Z\.\-L\. Nie, J\. Wang, and S\.\-M\. Hu, "Electric polarizabilities of CH4, CO, and O2 determined by an optical refractometer", Metrologia 63, 025007 \(2026\)

`Source record <https://github.com/LupoLab/optmat/blob/main/src/optmat/data/sources/zhao_2026.toml>`__ · :doc:`Catalogue </the-data/sources>` · :doc:`Review register </register>`

DOI: `10\.1088/1681\-7575/ae4c90 <https://doi.org/10.1088/1681-7575/ae4c90>`__

**Source kind:** measurement

**Recorded technique:** Fabry\-Perot gas refractometer \(USTC\)\: 10 cm ULE cavity \(mirror reflectivity ~99\.9 %, FSR 1\.5 GHz, mode linewidth ~0\.4 MHz\) in a vacuum chamber in a temperature\-stabilised jacket at about 297\.53 K \(NIM\-calibrated platinum resistance thermometer, 5 mK\); a 1566 nm fibre laser \(\<10 kHz\) Pound\-Drever\-Hall locked to a cavity mode, the absolute mode frequency counted against an ultra\-stable reference laser \(drift \< 0\.1 Hz/s\)\. n \- 1 = Delta nu/nu\_f \+ Delta p \(1/\(3K\) \+ d\) \(Eq\. 1\), the bulk modulus K = 3\.0822e10 Pa and the mirror\-deformation coefficient d = \-2\.0293e\-13 Pa^\-1 calibrated by measuring nitrogen's refractive index with A\_eps\(N2\) = 4\.38705\(16\) cm^3/mol \(Nie et al\. 2025, Ref\. 12\)\. Pressure from an Inficon CDGSci 1000 Torr capacitance gauge calibrated against a Fluke PG7601 piston gauge \(11 ppm\) and the optical pressure gauge, u = sqrt\(\(20e\-6 p\)^2 \+ \(1\.5 Pa\)^2\) below 100 kPa\. Gases CH4 and CO 99\.999 %, O2 99\.9995 %\. Pressure points 2\-100 kPa, several repeated runs; the molar polarization at each point from Eq\. \(2\) with the B\_T, B\_eps and A\_mu of Table 1; the weighted mean of the points \(pp\. 3\-6\)\.

**Materials in structured entries:** CH4, CO, O2

**Dataset quantities:** cauchy\_moment, molar\_refractivity

**Contents:** 17 datasets; 0 formulas.

Curation notes
--------------

Page numbers are the library pdf pages \(pdf page 1 is the publisher's cover, paper page 1 is pdf page 2\)\. CO \(curated since 2026\-09\-25\) is treated like CH4 below\.

WHAT IS MEASURED AND WHAT IS PRINTED\. The refractometer measures n \- 1 at 1566 nm \(vacuum wavelength\: 'omega = 45\.563 978 23/lambda, where lambda is the vacuum wavelength', p\. 4\)\. Eq\. \(2\) \(p\. 4\), p/RT = 2\(n \- 1\)/\(3\(A\_eps \+ A\_mu\)\) \+ \(n \- 1\)^2 \[\.\.\.\] \+ O\(n \- 1\)^3, reduces it to the refractive molar polarization A\_eps'\(omega\) \+ A\_mu; the authors subtract A\_mu \(Table 1\: CH4 \-17\.4\(8\)e\-6, O2 3449\(34\)e\-6 cm^3/mol, Refs\. 37\-39\) and convert the dynamic A\_eps'\(omega\) to the static A\_eps with Eq\. \(3\), A\_eps' = A\_eps \+ \(4 pi/3\) N\_A a0^3 \(1 \+ m\_e/m\_w\)^3 \[S\(\-4\) omega^2 \+ S\(\-6\) omega^4 \+ S\(\-8\) omega^6\], using the dipole sums of Table 1 \(CH4 from Olney et al\. 1997, Ref\. 29; O2 from Kumar and Thakkar 2011, Ref\. 31, identical to kumar\_2011's Table I 'This work' values; CO from Kumar and Meath 1994, Ref\. 30\)\. Only the static A\_eps is printed \(Table 3, abstract\)\: the measured 1566 nm values are not\. The datasets A\_R\_1566\_\* are therefore RECONSTRUCTED by tools/extract/zhao\_2026\.py, which inverts the authors' conversion exactly \(A\_R\(1566\) = A\_eps \+ dispersion sum \+ A\_mu; see the script for the constants, the omitted \(1 \+ m\_e/m\_w\)^3 factor, \< 0\.5 ppm, and the \+\-2 ppm from the nominal '1566 nm'\)\. The dispersion sum is 0\.019768 cm^3/mol for CH4 \(0\.31 %\), 0\.011080 for O2 \(0\.28 %\) and 0\.015351 for CO \(0\.31 %\)\.

WHAT THE STATIC VALUES INCLUDE\. The conversion subtracts only the electronic dispersion \(the S\(k\) are electronic dipole sums\); it makes no vibrational correction\. So the printed 'static' A\_eps is the electronic static polarizability \(vibrationally averaged, at 297\.5 K\) PLUS the vibrational \(infrared\) response at 1566 nm, which is negative above the fundamentals\: for CH4 about \-0\.029 au \(\-0\.011 cm^3/mol, \-0\.17 %\) from the HITRAN bands \(optmat\.gas\.infrared\); none for O2 \(no dipole\-allowed vibration\)\. It does NOT include the static vibrational polarizability that a dielectric \(DP\) measurement sees \(CH4\: 0\.240 au = 0\.090 cm^3/mol by HITRAN\)\. The authors say 'the RI method essentially measures the electronic part of the molecular polarizability' \(p\. 6\) and correct the CO literature for Bishop and Cheung's vibrational contribution and for CO's orientation term, but compare CH4 with Hohm's DP value directly \('we consider the dynamic contribution from omega to be approximately zero', p\. 5\) without a vibrational correction\. For O2 the DP value \(May et al\. 2008\) is directly comparable \(no infrared\-active vibration; the DP measures epsilon, without A\_mu\)\. Temperature\: CH4's A\_eps depends on it by 'approximately 5\-10 ppm per K' \(p\. 6, citing Hohm\)\.

UNCERTAINTY \(Table 2, p\. 5; relative, ppm, k = 1\)\: T 16, P 25 \(at 1 bar\), S\(i\) 9 \(CH4\) / 28 \(O2\), B \(B\_T and B\_eps\) 28 / 11, A\_mu 0\.6 / 8, statistical 14 / 17, gas purity 10 / 5, outgassing 0\.1 / 0\.2, cavity thermal expansion \< 0\.1, optical frequency \< 0\.1; total 45 \(CH4\), 46 \(O2\) \(CO 49\)\. The table's CH4 total reproduces the root sum of squares \(45\.2\); O2's is 46\.5\. The reconstructed A\_R\(1566\) keeps all but the S\(i\) and A\_mu lines\: 44\.3 ppm \(CH4\), 36\.3 ppm \(O2\), 37\.8 ppm \(CO; CO's total, 48\.9, is the root sum of squares of its column\)\. Resonance check\: 'both CO and CH4 have resonant absorption in the near\-infrared region'; a 30 GHz laser offset changed CO's result by 9e\-5 cm^3/mol, 'less than 20 ppm' \(p\. 5\)\.

CARBON MONOXIDE \(section 3\.2, pp\. 6\-7\)\. As for CH4, the printed static 4\.88146\(24\) cm^3/mol \(49 ppm\) is the 1566 nm value less the electronic dispersion of Kumar and Meath's sums \(Table 1, reproduced here\) and A\_mu \(\-15\.65e\-6 cm^3/mol\)\: it contains the electronic polarizability and the \(negative\) infrared response of CO at 1566 nm, not the static vibrational polarizability\. The authors compare with literature values reduced to the electronic part\: they subtract Bishop and Cheung's vibrational contribution, 20\(1\) x 10^\-43 C^2 m^2 J^\-1 \(0\.1213 au, 0\.0453 cm^3/mol; Ref\. 44 = bishop\_1982\) and, for the dielectric value of Tsankova et al\. \(2018, Ref\. 10\), the orientation term of mu\_e = 0\.107\(1\) D, interpolating their 255, 273, 293 and 313 K data to 297 K\. The text does not say which literature values received the vibrational subtraction \(the DP value certainly; the RI value should not need it\)\. The RI \(Hohm 2013\) and DOSD \(Kumar and Meath 1994\) values print uncertainties of 0\.26 and 0\.53 cm^3/mol \(5 % and 11 %\), implausibly large for those methods\: possibly the digits 4\.8826 and 4\.8953 misread as value\(uncertainty\)\. Hohm 2013 \(now curated, hohm\_2013\) prints CO 13\.04 \+\- 0\.07 au \(RI mean\) and 13\.08 \+\- 0\.15 au \(DOSD, his Ref\. 97, Jhanwar and Meath 1982\), 4\.874\(26\) and 4\.889\(56\) cm^3/mol\: both uncertainties here look one decade too large; taken as printed\. In au the three are 13\.055, 13\.077 \(DP\) and 13\.082 \(DOSD\), against this work's 13\.059\. Kumar and Meath 1994 is curated since \(kumar\_1994\)\: its S\(\-2\) = 13\.08 gives 4\.889 cm^3/mol, so the '4\.8953' reading of 4\.89\(53\) is not supported; the sums of Table 1 equal its Table 1 \(kumar\_meath\_1994\_ moments\_CO\)\.

INCONSISTENCIES IN THE PAPER \(not errata of extracted values\)\: Table 3's caption and the text of p\. 5 say 'CO2' for CO; sections 3\.2 \(CO\) and 3\.3 \(O2\) give the uncertainties as 46 and 49 ppm and cite figures 2\(f\) and 2\(e\), both swapped against Table 2, the abstract and the figure caption \(CO 49 ppm, \(e\); O2 46 ppm, \(f\)\); O2's printed 3\.95819\(20\) is 50\.5 ppm, not the 46 ppm of Table 2 \(it would be \(18\)\); Eq\. \(2\)'s second\-order bracket as printed, \(A\_eps^2 \+ 4B\_eps \+ 6A\_eps \+ A\_mu\), looks garbled \(not used here\)\.

Not extracted\: Table 1's A\_mu, B\_T \(a density virial\: no quantity\) and B\_eps \(CH4 7\.29\(32\), O2 \-0\.305\(28\) cm^6/mol^2; 'B\_eps values are from \[34\-36\]', which reference for which gas and at what temperature is not said; CO 7\.97\(40\), B\_T \-8\.5\(2\) cm^3/mol\); the per\-pressure points \(figure 2 only\)\.

**Recorded bibliographic identity status:** VALIDATED\_WITH\_WARNINGS. This concerns identification of the source; it does not establish the scientific correctness of its contents.

Datasets
--------

zhao\_2026/A\_R\_1566\_CH4
~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "A_R_1566_CH4",
     "material": "CH4",
     "file": "CH4/zhao_2026__A_R_1566_CH4.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "primary",
     "uncertainty": {
       "column": true,
       "level": "1 sigma"
     },
     "parameters": {
       "temperature_k": 297.53
     }
   }

RECONSTRUCTED \(not printed\)\: the refractive molar polarization A\_eps'\(omega\) \+ A\_mu at 1566 nm \(vacuum\) and 297\.53 K that the refractometer measured, = Table 3's static 6\.44034 \+ \(4 pi/3\) N\_A a0^3 \[S\(\-4\) w^2 \+ S\(\-6\) w^4 \+ S\(\-8\) w^6\] \(Table 1, Olney's sums; w = 45\.56397823/1566\) \+ A\_mu \(\-17\.4e\-6\), computed by tools/extract/zhao\_2026\.py\. Includes everything n contains at 1566 nm\: the electronic polarizability and the \(negative\) infrared response\. Uncertainty\: Table 2 without the S\(i\) and A\_mu lines, 44\.3 ppm, one sigma\.

zhao\_2026/A\_R\_1566\_O2
~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "A_R_1566_O2",
     "material": "O2",
     "file": "O2/zhao_2026__A_R_1566_O2.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "check",
     "uncertainty": {
       "column": true,
       "level": "1 sigma"
     },
     "parameters": {
       "temperature_k": 297.53
     }
   }

RECONSTRUCTED \(not printed\), as A\_R\_1566\_CH4\: 3\.95819 \+ 0\.011080 \(Kumar and Thakkar's sums\) \+ A\_mu 3449e\-6 = 3\.972719 cm^3/mol at 1566 nm, 297\.53 K; uncertainty 36\.3 ppm \(Table 2 without S\(i\) and A\_mu\)\. A check, not primary\: A\_mu is 870 ppm of the value and whether O2's paramagnetic susceptibility belongs in the optical refractivity is unresolved\. egan\_2026 says oxygen's optical A\_R excludes it; moved to Egan et al\.'s 1542\.383 nm with the same sums, the reconstruction \(with A\_mu, as Eq\. 2 is printed\) gives 3\.973063, 1026 ppm above their 3\.968990\(7\) cm^3/mol \(303 K\), the static value plus dispersion without A\_mu 3\.969614, 157 ppm above\. Neither can be verified from the paper\.

zhao\_2026/static\_CH4
~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "static_CH4",
     "material": "CH4",
     "file": "CH4/zhao_2026__static_CH4.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "check",
     "uncertainty": {
       "column": true,
       "level": "1 sigma"
     },
     "parameters": {
       "temperature_k": 297.53
     }
   }

Table 3 'This work'\: A\_eps = 6\.44034\(30\) cm^3/mol \(abstract; 45 ppm, k = 1\), derived from the 1566 nm measurement with Olney's electronic dipole sums \(Eq\. 3\)\. Not independent of A\_R\_1566\_CH4\: a check\. ELECTRONIC ONLY\: it contains no static vibrational polarizability \(a dielectric value would add about 0\.090 cm^3/mol, HITRAN's 0\.240 au\), and it still carries the infrared response at 1566 nm \(about \-0\.011 cm^3/mol, HITRAN\), which the conversion does not remove\: the electronic static polarizability is about 0\.17 % above it\. At 297\.53 K\.

zhao\_2026/static\_O2
~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "static_O2",
     "material": "O2",
     "file": "O2/zhao_2026__static_O2.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "check",
     "uncertainty": {
       "column": true,
       "level": "1 sigma"
     },
     "parameters": {
       "temperature_k": 297.53
     }
   }

Table 3 'This work'\: A\_eps = 3\.95819\(20\) cm^3/mol \(abstract; Table 2 gives 46 ppm, the printed \(20\) is 50\.5 ppm\), derived from the 1566 nm measurement by subtracting A\_mu = 3449e\-6 cm^3/mol and Kumar and Thakkar's electronic dispersion\. A check \(not independent of A\_R\_1566\_O2\)\. O2 has no dipole\-allowed vibration, so this is the static electric polarizability; the authors find it agrees with May et al\.'s dielectric 3\.9582\(2\) interpolated to 297 K 'at the 10^\-5 level' \(p\. 7\)\. At 297\.53 K\.

zhao\_2026/hohm\_2013\_ri\_CH4
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "hohm_2013_ri_CH4",
     "material": "CH4",
     "file": "CH4/zhao_2026__hohm_2013_ri_CH4.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "reproduced",
     "reproduced_from": [
       "hohm_2013"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

Table 3 'RI'\: 6\.445\(10\) cm^3/mol, Hohm's \(2013\) static value from refractive\-index measurements \(a summary, 'mostly \.\.\. averages from various literature sources', p\. 5\)\: an optical extrapolation to zero frequency, so electronic only\. Uncertainty level not stated\. Temperature not stated\. Hohm 2013 \(penta\-atomic table, RI 'Mean value'\) prints 17\.240 \+\- 0\.026 au, which is 6\.4444\(97\) cm^3/mol\: Zhao et al\.'s 6\.445 is 1 in the last digit higher \(0\.01 %; checked 2026\-09\-26\)\.

zhao\_2026/hohm\_2013\_dp\_CH4
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "hohm_2013_dp_CH4",
     "material": "CH4",
     "file": "CH4/zhao_2026__hohm_2013_dp_CH4.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "reproduced",
     "reproduced_from": [
       "hohm_2013"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

Table 3 'DP'\: 6\.454\(17\) cm^3/mol, Hohm's \(2013\) static value from dielectric\-permittivity measurements \(GHz range\)\. A dielectric value of CH4 should include the vibrational polarizability \(HITRAN 0\.240 au = 0\.090 cm^3/mol\); whether Hohm's value does, or was corrected, is not said here\: its excess over the RI value, 0\.009\(20\) cm^3/mol, is smaller\. Hohm 2013 \(penta\-atomic table, DP 'Mean value'\) answers it\: alpha\_el = 17\.266 \+\- 0\.045 au from alpha\_el \+ alpha\_vib = 17\.496 \+\- 0\.025 au less alpha\_vib = 0\.23 au \(his Ref\. 16, Bishop and Cheung 1982 = bishop\_1982\); 17\.266 au is 6\.4541\(168\) cm^3/mol, so Zhao et al\.'s 6\.454\(17\) is Hohm's ELECTRONIC value, vibration already subtracted \(checked 2026\-09\-26\)\. Uncertainty level not stated\. Temperature not stated\.

zhao\_2026/may\_2008\_O2
~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "may_2008_O2",
     "material": "O2",
     "table": "text",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "reproduced",
     "reproduced_from": [
       "may_2008"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

2 inline points in the source record.

p\. 7\: May et al\.'s dielectric \(cross\-capacitor\) static A\_eps of O2, 'the results at 293 and 323 K are 3\.9582\(2\) cm^3/mol and 3\.95824\(7\) cm^3/mol' \(row = temperature in K as printed; May et al\. also measured at 273 K, value not quoted\)\. A dielectric measurement sees epsilon only\: no magnetic term; O2 has no infrared\-active vibration, so this is the static electric polarizability\. Uncertainty level not stated here\.

zhao\_2026/may\_2008\_297K\_O2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "may_2008_297K_O2",
     "material": "O2",
     "file": "O2/zhao_2026__may_2008_297K_O2.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "check",
     "reproduced_from": [
       "may_2008"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

Table 3 'DP'\: 3\.9582\(2\) cm^3/mol, Zhao et al\.'s interpolation of May et al\.'s 293 and 323 K values \(may\_2008\_O2\) to 297 K, 'taking the uncertainty from the 293 K result as reference' \(p\. 7\)\. Derived from may\_2008\_O2\: a check\.

zhao\_2026/kumar\_2011\_dosd\_O2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "kumar_2011_dosd_O2",
     "material": "O2",
     "file": "O2/zhao_2026__kumar_2011_dosd_O2.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "reproduced",
     "reproduced_from": [
       "kumar_2011"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

Table 3 'DOSD'\: 3\.959\(11\) cm^3/mol \(Ref\. 31, Kumar and Thakkar 2011\)\: their S\(\-2\) = 10\.59 au \(kumar\_2011/o2\) times \(4 pi/3\) N\_A a0^3 = 3\.9586 cm^3/mol\. Static electronic \(a dipole sum of the electronic distribution\)\.

zhao\_2026/olney\_1997\_moments\_CH4
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "olney_1997_moments_CH4",
     "material": "CH4",
     "file": "CH4/zhao_2026__olney_1997_moments_CH4.csv",
     "table": "tbl_632ce5af228b",
     "quantity": "cauchy_moment",
     "unit": "au",
     "abscissa": "order",
     "abscissa_unit": "1",
     "use": "reproduced",
     "reproduced_from": [
       "olney_1997"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

Table 1\: CH4 dipole sums S\(\-4\) = 62\.22\(19\), S\(\-6\) = 295\.0\(57\), S\(\-8\) = 1660\(54\) au, from Olney et al\. \(caption\: 'Dipole sum terms \[29\-31\]'; CH4 is Ref\. 29 by the text, p\. 5\)\. Electronic sums, used for the 1566 nm to static conversion\. Uncertainty level not stated\. The three values are digit\-identical to olney\_1997's Table 3 CH4 'Expt' row \(olney\_1997/moments\_CH4, checked 2026\-09\-26\), whose scale is renormalised to Hohm's \(1993\) polarizability; Olney et al\. print no uncertainties, so the parenthesised ones \(0\.3, 1\.9, 3\.3 %\) are Zhao et al\.'s own\. Re\-pointed to olney\_1997 \(was a citation 'not in the library'\)\.

zhao\_2026/kumar\_2011\_moments\_O2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "kumar_2011_moments_O2",
     "material": "O2",
     "file": "O2/zhao_2026__kumar_2011_moments_O2.csv",
     "table": "tbl_632ce5af228b",
     "quantity": "cauchy_moment",
     "unit": "au",
     "abscissa": "order",
     "abscissa_unit": "1",
     "use": "reproduced",
     "reproduced_from": [
       "kumar_2011"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

Table 1\: O2 dipole sums S\(\-4\) = 34\.81\(35\), S\(\-6\) = 238\.6\(23\), S\(\-8\) = 2224\(66\) au, Kumar and Thakkar \(2011, Ref\. 31\)\: identical to kumar\_2011/o2 \('This work' of their Table I\); the parenthesised values are that paper's 1 % \(k \>= \-6\) and 3 % \(k = \-8\) estimates\.

zhao\_2026/A\_R\_1566\_CO
~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "A_R_1566_CO",
     "material": "CO",
     "file": "CO/zhao_2026__A_R_1566_CO.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "primary",
     "uncertainty": {
       "column": true,
       "level": "1 sigma"
     },
     "parameters": {
       "temperature_k": 297.53
     }
   }

RECONSTRUCTED \(not printed\), as A\_R\_1566\_CH4\: Table 3's static 4\.88146 \+ \(4 pi/3\) N\_A a0^3 \[S\(\-4\) w^2 \+ S\(\-6\) w^4 \+ S\(\-8\) w^6\] \(Table 1, Kumar and Meath's sums, 0\.015351\) \+ A\_mu \(\-15\.65e\-6\) = 4\.896795 cm^3/mol at 1566 nm \(vacuum\), 297\.53 K\. Includes everything n contains at 1566 nm, the electronic polarizability and the \(negative\) infrared response; CO has 'resonant absorption in the near\-infrared region'; the authors bound its effect on this value by a 30 GHz laser offset test, \< 20 ppm \(p\. 5\)\. Uncertainty\: Table 2 without the S\(i\) and A\_mu lines, 37\.8 ppm, one sigma\.

zhao\_2026/static\_CO
~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "static_CO",
     "material": "CO",
     "file": "CO/zhao_2026__static_CO.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "check",
     "uncertainty": {
       "column": true,
       "level": "1 sigma"
     },
     "parameters": {
       "temperature_k": 297.53
     }
   }

Table 3 'This work'\: A\_eps = 4\.88146\(24\) cm^3/mol \(abstract; 49 ppm, k = 1\), derived from the 1566 nm measurement with Kumar and Meath's electronic dipole sums \(Eq\. 3\)\. Not independent of A\_R\_1566\_CO\: a check\. ELECTRONIC ONLY in the authors' sense\: no static vibrational polarizability \(Bishop and Cheung's 0\.1213 au = 0\.0453 cm^3/mol would be added for a dielectric value\), but it still carries CO's infrared response at 1566 nm, which the conversion does not remove\. No orientation term \(an optical measurement\)\. At 297\.53 K\.

zhao\_2026/hohm\_2013\_ri\_CO
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "hohm_2013_ri_CO",
     "material": "CO",
     "file": "CO/zhao_2026__hohm_2013_ri_CO.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "reproduced",
     "reproduced_from": [
       "hohm_2013"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

Table 3 'RI'\: 4\.88\(26\) cm^3/mol, Hohm's \(2013\) static value from refractive\-index measurements, electronic only\. The printed uncertainty, 0\.26 cm^3/mol \(5 %\), is implausible for the method; possibly 4\.8826 misprinted as a value with uncertainty \(source notes\)\. Hohm 2013 \(heteronuclear diatomics table, RI 'Mean value'\) prints 13\.04 \+\- 0\.07 au = 4\.874\(26\) cm^3/mol\: the printed uncertainty is ten times Hohm's converted one and the value 0\.006 above it \(checked 2026\-09\-26\)\. Whether Zhao et al\. applied their vibrational subtraction to it is not said\. Level and temperature not stated\.

zhao\_2026/tsankova\_2018\_dp\_CO
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "tsankova_2018_dp_CO",
     "material": "CO",
     "file": "CO/zhao_2026__tsankova_2018_dp_CO.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "check",
     "reproduced_from": [
       "tsankova_2018"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     },
     "parameters": {
       "temperature_k": 297.0
     }
   }

Table 3 'DP'\: 4\.888\(45\) cm^3/mol, Tsankova et al\.'s dielectric measurements \(255\-313 K\) reduced by Zhao et al\. to the electronic part\: the orientation term of mu\_e = 0\.107\(1\) D and Bishop and Cheung's vibrational 20\(1\)e\-43 C^2 m^2 J^\-1 \(0\.0453 cm^3/mol\) subtracted, interpolated to 297 K \(pp\. 6\-7\)\. Derived, not Tsankova's value\: a check\. Level not stated\. Re\-pointed to tsankova\_2018 \(curated 2026\-10\-01; was a citation\)\: the value is \(alpha\_e \- 0\.020e\-40\) N\_A/\(3 eps0\) = 4\.8880 cm^3/mol from tsankova\_2018/alpha\_e\_CO \(2\.176e\-40 C m^2/V\), whose temperature\-independent alpha\_e needs no interpolation; the uncertainty 0\.045 is not Tsankova's \(0\.050 cm^3/mol at k = 2, 0\.025 at k = 1\)\.

zhao\_2026/kumar\_meath\_1994\_dosd\_CO
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "kumar_meath_1994_dosd_CO",
     "material": "CO",
     "file": "CO/zhao_2026__kumar_meath_1994_dosd_CO.csv",
     "table": "tbl_5032bd285fb3",
     "quantity": "molar_refractivity",
     "unit": "cm3/mol",
     "abscissa_unit": "nm",
     "use": "reproduced",
     "reproduced_from": [
       "kumar_1994"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

Table 3 'DOSD'\: 4\.89\(53\) cm^3/mol \(Ref\. 30\), a static electronic dipole sum S\(\-2\) \(13\.08 au with the package's constants\)\. The printed uncertainty, 0\.53 cm^3/mol \(11 %\), is implausible for a constrained DOSD; possibly 4\.8953 misprinted \(source notes\)\. kumar\_1994 \(curated since\) prints S\(\-2\) = 13\.08 \(Tables 1, 3\), which gives \(4 pi/3\) N\_A a0^3 x 13\.08 = 4\.889 cm^3/mol, not 4\.8953 \(that would need 13\.096\)\: the '4\.8953' reading is not supported by the original \(checked 2026\-09\-27\)\. Level not stated\.

zhao\_2026/kumar\_meath\_1994\_moments\_CO
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "kumar_meath_1994_moments_CO",
     "material": "CO",
     "file": "CO/zhao_2026__kumar_meath_1994_moments_CO.csv",
     "table": "tbl_632ce5af228b",
     "quantity": "cauchy_moment",
     "unit": "au",
     "abscissa": "order",
     "abscissa_unit": "1",
     "use": "reproduced",
     "reproduced_from": [
       "kumar_1994"
     ],
     "uncertainty": {
       "column": true,
       "level": "not stated"
     }
   }

Table 1\: CO dipole sums S\(\-4\) = 48\.26\(48\), S\(\-6\) = 292\.9\(29\), S\(\-8\) = 2308\(64\) au \(caption\: 'Dipole sum terms \[29\-31\]'; Ref\. 30 is Kumar and Meath's CO paper\)\. Electronic sums, used for the 1566 nm to static conversion\. Uncertainty level not stated\. Equal to kumar\_1994's Table 1 isotropic sums \(4\.826\(1\), 2\.929\(2\), 2\.308\(3\)\) \(checked 2026\-09\-27\); the original is curated since \(kumar\_1994/moments, use check\), so this copy is no longer the best available \(the fit's input is decided at review\)\. The parenthesised uncertainties are Zhao et al\.'s \(1 %, 1 %, 2\.8 %\); Kumar and Meath state \<~1 % for \-4 \<= k \< 1, 'increase slowly for k \< \-4'\.

Formulas
--------

No formulas are recorded.

Corrections
-----------

No dataset errata are recorded in this source record.

Formula corrections, where recorded, appear with their formulas above. Curation notes may also discuss corrections or unresolved interpretation. Consult the :doc:`review register </register>` for the checks and decisions.