JPH05296922A - Carbon isotope analyzing instrument - Google Patents

Abstract

PURPOSE:To provide a carbon isotope analyzing instrument which has high sensitivity and accuracy and, at the same time, can trace the carbon isotope ratio without receiving any influence from the spectrum of water, etc. CONSTITUTION:Objects to be analyzed, namely, <12>CO2 and <13>CO2 are put in a sample cell 2, and parts of the objects are absorbed by resonance by irradiating the objects with semiconductor laser light in a near infrared region. At the same time, residual light rays having different intensities from the objects are introduced to a lock-in amplifier 6 after detecting the light rays with a photodetector 5. The amplifier 6 detects the intensity ratio between the absorption spectrum of the light from the <12>CO2 when the emission wavelength of a semiconductor laser 1 is 6253.73+ or -0.2 [cm<-1>] and the light of the <13>CO2 when the emission wavelength is 6253.90 [cm<-1>].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon isotope analyzer which irradiates a sample substance containing a plurality of carbon isotopes with light and obtains the ratio of the isotopes based on the intensity ratio of the light absorption spectra.

[0002]

BACKGROUND OF THE INVENTION There are few isotopes in nature, and by tracing changes in these isotopes, diagnosis of diseases in the medical field, research of photosynthesis in the agricultural field, research on metabolism of plants, earth science. It can be used to trace ecosystems in the field.

Isotopes used for such applications include nitrogen and carbon. Particularly, in terms of carbon, carbon having a mass number of 12 (hereinafter abbreviated as ¹² C) and carbon having a mass number of 13 (hereinafter
Abbreviated as ¹³ C). Unlike the radioactive isotopes, these stable isotopes are free from radiation exposure and are easy to handle, so their use in the medical field is being actively studied.

FIG. 4 shows an example of an apparatus conventionally used as the above stable isotope analysis apparatus. In the figure, 10 is a lamp having a wide emission wavelength range in the infrared region, 11 is a sample cell, 12 is a sample gas inlet, 13 is a sample gas outlet, 14 is a dispersive spectrometer, 15 is a mirror, 16 is a diffraction grating, Reference numeral 17 is a slit, and 18 is a photodetector.

In this apparatus, the sample gas is introduced into the sample cell 11 through the sample gas inlet 12 and the sample gas outlet 1
Emitted from 3. The light emitted from the lamp 10 is the sample cell 1
1, and interacts with the sample gas in the sample cell 11 to partially absorb the resonance. The remaining light passes through the sample cell 11 and enters the dispersive spectroscope 14, the beam direction is changed by the mirror 15, and the diffraction grating 16 is irradiated with the changed beam direction. Then, the diffraction grating 16 performs wavelength dispersion, and the light intensity of the wavelength selected by the slit 17 is detected by the photodetector 18. Here, the selective wavelength is changed by continuously rotating the angle of the diffraction grating 16 in the θ direction, and the light absorption spectrum of the sample gas is measured.

In the measurement, carbon does not directly resonate with light in the infrared region, so carbon dioxide (CO ₂ ) is introduced into the sample cell 11 in advance and its spectrum is measured. Also, carbon dioxide ¹² CO ₂ and ¹³ CO
_{Since 2} has a mass difference, the light absorption frequency is slightly different. Therefore, rotate the diffraction grating 16 to change the angle θ.
The changes in the carbon isotope ratio can be traced by measuring the optical absorption spectra of ¹² CO ₂ and ¹³ CO ₂ almost at the same time and determining the ratio of their absorption intensities.

By the way, the fine structures (vibration / rotation spectra) of the optical absorption spectra of ¹² CO ₂ and ¹³ CO ₂ are as shown in FIGS. 4 (a) and 4 (b), respectively, and the difference between the spectra of both is small. Is. The spectrum width of this fine structure is 0.1 [c at a sample gas pressure of 760 Torr.
m ^-1 ], several 0.01 Torr is very narrow at about 0.01 [cm ^-1 ]. Further, since the natural abundance of ¹³ CO ^_2/12 CO ₂ is about 1%, the light absorption intensity of ¹² CO ₂ is than ¹³ CO ₂ 10
About 0 times stronger.

To accurately measure such a spectrum, a spectral resolution of 0.001 [cm ^-1 ] or more is required, but the conventional analytical apparatus has a spectral resolution of 1 [cm ^-1 ].
Since it is about the same and wider than the optical absorption spectrum width of CO ₂ gas, it is not possible to separate and measure each spectrum of the fine structure. As a result, the optical absorption spectra of carbon isotopes affect each other, and an accurate spectrum cannot be measured. Therefore, a spectrum in which the spectra of ¹² CO ₂ and ¹³ CO ₂ overlap each other as shown in FIG. 5 was measured.

[0009]

In such a spectrum influenced by each other, for example, even if the concentration of ¹² CO ₂ changes slightly, the spectrum of ¹³ CO ₂ is affected and a measurement error occurs. .. In conventional analyzers, the amount of overlap between the spectra is calculated and corrected based on the measured spectrum, but the amount of overlap between the spectra cannot be sufficiently removed by the correction, so changes in the isotope ratio can be traced accurately. Can not.

Further, the sample gas contains many impurities other than CO ₂ gas, and these impurities also absorb light, so that the optical absorption spectrum of the impurities is present in the vicinity of the spectrum of CO ₂ gas. It will be affected and cause a measurement error. It is necessary to increase the spectral resolution in order to remove the influence of the impurities as much as possible, but as described above, the conventional analyzer has a low spectral resolution.

Further, in order to detect a trace amount of change in carbon isotope, it is necessary to detect an optical absorption spectrum with high sensitivity. In the conventional analyzer described above, the slit 17
The sensitivity can be increased by widening the range, but the reciprocal relationship that the resolution becomes low is difficult, and it is difficult to achieve both sensitivity and accuracy.

An object of the present invention is to provide a carbon isotope analyzer capable of tracing the carbon isotope ratio with high sensitivity and accuracy without being affected by the optical absorption of carbon isotopes, the spectrum of impurities, and the influence of disturbance. To provide.

[0013]

According to the present invention, a semiconductor laser in the near-infrared region having a very narrow emission spectrum width is used as a wavelength tunable light source, and this is irradiated onto a sample gas to produce ¹² CO ₂ and ¹³ CO 2.
The intensity ratio of the light absorption spectrum with ₂ is detected.

More specifically, AlGaAs or InGaAs
Near-infrared semiconductor lasers using P-based materials are used for optical communication,
It has been energetically researched and developed for optical information processing, and it is compact, highly efficient, and highly reliable. Infrared semiconductor lasers made of lead-salt-based materials do not oscillate at room temperature, so a large cooling machine using liquid helium or liquid nitrogen is required. If the temperature of the semiconductor laser is controlled by the above, it becomes a wavelength tunable light source.

By using the near-infrared region semiconductor laser having such practically excellent characteristics, the entire apparatus can be made extremely small, easy to handle, and highly reliable. Since the oscillation spectrum width of this kind of semiconductor laser in the near infrared region is very narrow, from 0.0003 to 0.002 [cm ^-1 ], by sweeping the oscillation wavelength of this semiconductor laser, each spectrum of CO ₂ vibration and rotation can be obtained. Can be easily measured.

However, each of the measurable vibration and rotation spectra includes a spectrum suitable for isotope ratio measurement and a spectrum not suitable for isotope ratio measurement. Therefore, when measuring the isotope ratio, it is necessary to select an optimum spectrum that satisfies the following conditions.

(1) Since the absorption intensity of the optical absorption spectrum of ¹³ CO ₂ is weaker by about two orders of magnitude than the absorption intensity of ¹² CO ₂ , ¹³ C
A spectrum having a high optical absorption intensity of O ₂ and not affected by the spectrum of ¹² CO ₂ is selected.

(2) The light absorption spectrum of CO ₂ measured in the near infrared region is the vibration and rotation spectrum of the CO ₂ molecule, and other weak vibrations other than the desired vibration and rotation spectrum, Since there are many rotation spectra, select a spectrum that is not affected by other vibration and rotation spectra.

(3) Since the optical spectra of ¹² CO ₂ and ¹³ CO ₂ are measured almost at the same time and the isotope ratio is determined from the absorption intensity ratio, the absorption spectra of ¹³ CO ₂ and ¹² CO ₂ are suitable. Be close to each other at regular intervals.

(4) Since the sample gas contains many impurities, especially water, in addition to the isotope gas, a spectrum that is not affected by the optical absorption spectrum of this water is selected.

As a result of searching the spectrum satisfying the above conditions in the near infrared region, it was found that the spectrum was very small.

Therefore, according to the present invention, in the isotope analyzer for detecting the isotope ratio of the test substance in which a plurality of carbon isotopes ¹² CO ₂ and ¹³ CO ₂ are mixed based on the light absorption spectrum intensity ratio, An infrared semiconductor laser, a means for sweeping the oscillation wavelength of this semiconductor laser, a frequency modulation means for frequency-modulating this semiconductor laser, and a test object emitted from this semiconductor laser in which the plurality of carbon isotopes are mixed. It has a photodetector for detecting the passing laser beam, and a lock-in amplifier for detecting the matching between the modulation frequency obtained by the frequency modulating means and the signal frequency of the laser beam detected by the photodetector. , The emission wavelength of the semiconductor laser is
The optical absorption spectrum of ¹² CO ₂ when the wave number is 6253.73 ± 0.2 [cm ^-1 ] and the emission wavelength is 6253.90 [cm ^-1 ]
The intensity ratio with the light absorption spectrum of ¹³ CO ₂ at that time was detected.

In addition to the combination of the emission wavelengths of the semiconductor lasers, the combination of each left column and right column of Table 1 can be used to detect the light absorption spectrum intensity ratio.

[0024]

[Table 1]

[0025]

The carbon isotope analysis device of the present invention sweeps the oscillation wavelength which is not influenced by the mutual influence of ¹² CO ₂ and ¹³ CO ₂ of the semiconductor laser in the near infrared region and moisture, and is modulated by the frequency modulation means. The laser light is made incident on the test object in which the carbon isotope is mixed. The incident laser light interacts with the carbon isotope and a part thereof is resonantly absorbed. Then, the residual light is detected by the photodetector, and the light absorption spectra of ¹² CO ₂ and ¹³ CO ₂ are measured by the lock-in amplifier.

Since there is a mass difference between ¹² CO ₂ and ¹³ CO ₂ , the light absorption frequencies are slightly different. Therefore, the changes in the carbon isotope ratio can be traced by measuring the respective light absorption spectra almost at the same time and determining the ratio of the absorption intensities of the two.

The emission wavelength of the semiconductor laser is 6253.73.
Optical absorption spectrum of ¹² CO ₂ at ± 0.2 [cm ^-1 ] and ¹³ CO at the same emission wavelength of 6253.90 [cm ^-1 ]
Combination of the _second light absorption spectrum, and a combination of the left column and the right column of Table 1, are close at appropriate intervals, ¹³ C
The optical absorption spectrum of O ₂ is not affected by the spectrum of ¹² CO ₂ .

[0028]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a carbon isotope analyzer to which the present invention is applied. 1 is a semiconductor laser in the near infrared region, 2 is a sample gas containing ¹² CO ₂ and ¹³ CO ₂ mixed therein. A sample cell, 3 is a sample gas inlet, 4 is a sample gas outlet, 5 is a photodetector, 6 is a lock-in amplifier, 7 is a temperature control unit for sweeping the wave number of the semiconductor laser 1, 8
Is a current control unit for controlling the optical output of the semiconductor laser 1, and 9 is an oscillator for giving a modulation frequency to the current control unit 8.

In the apparatus having the above structure, the semiconductor laser 1 in the near infrared region continuously oscillates at room temperature, and becomes a wavelength tunable light source by sweeping the temperature or driving current of the semiconductor laser 1. The emission wave number of the semiconductor laser 1 is swept through the temperature by the temperature control unit 7, and the wave number is 6253.90 [cm ⁻¹ ] and the wave number 6253.73 [cm
^-1 ] The vicinity is continuously swept. Further, the drive current of the semiconductor laser 1 is controlled by the current controller 8 so as to obtain an appropriate light output. Further, it is current-modulated by the signal of the oscillator 9 and slightly frequency-modulated.

The laser light from the semiconductor laser 1 thus wavenumber-swept and frequency-modulated is incident on the sample cell 2, where it interacts with the ¹² CO ₂ gas and ¹³ CO ₂ gas in the cell. Partly absorbed. The laser light emitted from the sample cell 2 is detected by the photodetector 5. Of the detected optical signals, only the signal synchronized with the oscillator 9 is detected by the lock-in amplifier 6. As a result, the drift of the light intensity of the semiconductor laser 1 can be removed, and a signal with a good S / N ratio can be detected.

The optical signal thus detected is the first derivative of the light absorption intensity. Therefore, in the infrared absorption spectrum diagram of FIG. 2 formed by this example, the peak value of both detection signals at the wave number of 6253.90 [cm ⁻¹ ] and the wave number of 6253.73 [cm ⁻¹ ] or the area of absorption was obtained. be determined the ratio of the absorption Te, mixed in the sample cell 2 ¹² CO ₂ gas and ¹³
The ratio with CO ₂ gas, that is, the isotope ratio, can be easily obtained.

Further, if only the frequency component twice the signal oscillated by the oscillator 9 is detected by the lock-in amplifier 6, the second-order differential shape of the light absorption intensity can be measured. Same as above
If the ratio of the peak values of both detection signals at 6253.90 [cm ^-1 ] and wave number 6253.73 [cm ^-1 ] is calculated, the isotope ratio can be easily calculated. Moreover, in this method, since the second-order differential shape of the light absorption intensity is measured, the first-order change and second-order change emitted from the semiconductor laser 1 are canceled, and the isotope ratio can be measured with higher accuracy.

In the present embodiment, the light emission wavelength of the semiconductor laser 1 is 6253.7 for detecting the light absorption spectrum intensity ratio.
The absorption spectrum of ¹² CO ₂ at 3 ± 0.2 [cm ^-1 ] and ^{13 at the} same emission wavelength of wave number 6253.90 [cm ^-1 ]
The light absorption spectrum of CO ₂ was used, but in addition to this combination, the light absorption spectrum of ¹² CO ₂ when the emission wavelength is 6254.67 ± 0.2 [cm ⁻¹ ] and the emission wavelength is 625
The absorption spectrum of ¹³ CO ₂ at 5.14 ± 0.2 [cm ^-1 ], when the emission wavelength is 6255.58 ± 0.2 [cm ^-1 ]
¹² CO ₂ optical absorption spectrum and emission wavelength 6255.1
^{4 ± 0.2 [cm -1] 13} CO 2 of the light absorption spectrum when the light emission wavelength when the wavenumber 6257.29 ± 0.2 [cm ^{-1] 12}
The light absorption spectrum of CO ₂ and the emission wavelength of wave number 6257.51
Optical absorption spectrum of ¹³ CO ₂ at ± 0.2 [cm ⁻¹ ],
¹² CO when emission wavelength is 6258.88 ± 0.2 [cm ^-1 ]
₂ light absorption spectrum and the emission wavelength is wave number 6258.64 ± 0.
2 [cm ^-1] optical absorption spectrum, and the light absorption spectrum of the ¹² CO ₂ when the emission wavelength wavenumber 6261.01 ± 0.2 [cm ^-1], emission wavelength wavenumber 6,260.80 ± 0.2 of ¹³ CO ₂ in the case of
[Cm ^{-1] 13} CO ₂ of the light absorption spectrum when the, the light absorption spectrum of the ¹² CO ₂ when the emission wavelength wavenumber 6261.65 ± 0.2 [cm ^-1], emission wavelength wavenumber 6261.83 ± 0.2 [cm
^-1 ], the optical absorption spectrum of ¹³ CO ₂ at an emission wavelength of 6252.77 ± 0.2 [cm ^-1 ] and the optical absorption spectrum of ¹² CO ₂ at an emission wavelength of 6252.77 ± 0.2 [cm ^-1 ]
Absorption spectrum of ¹³ CO ₂ and emission wavelength
6251.77 ± 0.2 [cm ^-1] and the light absorption spectrum of the ¹² CO ₂ in the case of, ¹³ CO ₂ in the optical absorption spectrum when the emission wavelength wavenumber 6251.32 ± 0.2 [cm ^-1], emission wavelength wavenumber 624
The optical absorption spectrum of ¹² CO ₂ at 9.67 ± 0.2 [cm ^-1 ] and the optical absorption spectrum of ¹³ CO _{2 at} the emission wavelength of 6249.98 ± 0.2 [cm ^-1 ], the emission wavelength of 6228.6
The absorption spectrum of ¹² CO ₂ at 9 ± 0.2 [cm ^-1 ] and ^{13 at the} emission wavelength of wave number 6228.44 ± 0.2 [cm ^-1 ]
CO ₂ light absorption spectrum, emission wavelength is wavenumber 6231.72 ±
The optical absorption spectrum of ¹² CO ₂ at 0.2 [cm ⁻¹ ],
¹³ CO when the emission wavelength is 6232.03 ± 0.2 [cm ^-1 ]
₂ light absorption spectrum, emission wavelength wave number 6233.19 ± 0.2
[Cm ^-1] and ¹² CO ₂ of the light absorption spectrum when the, ¹³ CO ₂ in the optical absorption spectrum when the emission wavelength wavenumber 6233.77 ± 0.2 [cm ^-1], emission wavelength wavenumber 6226.35 ± 0.2 [cm
^-1] and ¹² CO ₂ of the light absorption spectrum when the, ¹³ CO ₂ in the optical absorption spectrum when the emission wavelength wavenumber 6226.59 ± 0.2 [cm ^-1], emission wavelength wavenumber 6223.13 ± 0.2 [cm ^-1]
The light absorption spectrum of ¹² CO ₂ at that time and the light absorption spectrum of ¹³ CO ₂ at an emission wavelength of wave number 6222.79 ± 0.2 [cm ⁻¹ ] may be used, and the same preferable results are obtained as described above.

Further, in the present embodiment, the temperature of one semiconductor laser 1 is controlled to sweep the emission wavelength thereof, but the driving current of the semiconductor laser 1 may be controlled to sweep near the respective wave numbers. Alternatively, two semiconductor lasers 1 may be used to simultaneously oscillate the laser beams in the vicinity of the respective wave numbers, and make the laser beams enter the sample cell 2 alternately.

Further, although the frequency modulation of the semiconductor laser 1 is performed by current modulation, an EO modulator (Electro-
Opyic Modulator) may be provided for modulation.

As described above, in the present embodiment, the lock-in amplifier has two kinds of spectral intensities, which are strong in light absorption intensity of ¹³ CO ₂ gas and which are not affected by mutual influence with ¹² CO ₂ gas or moisture. Since the measurement is performed in No. 6, the influence of disturbance can be removed.

Further, the semiconductor laser light in the near infrared region, which has a very narrow emission spectrum width, is small and has high reliability, is used as a wavelength tunable light source, and the wavelength is used almost 100% to measure with the lock-in amplifier 6. Therefore, the isotope ratio can be measured with high accuracy and high sensitivity, and a highly reliable carbon isotope analyzer can be realized.

[0039]

As described above in detail, in the carbon isotope analysis apparatus of the present invention, a semiconductor laser having a small size, high reliability, and a very narrow spectral width in the near infrared region is used as a wavelength tunable light source, Moreover, since the emission wavelength was set to a specific wave number that was reasonably close to each other, the influence of mutual absorption of carbon isotopes and the influence of the spectrum of water and the like,
The isotope ratio of ¹² CO ₂ and ¹³ CO ₂ can be traced with high accuracy and high sensitivity.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a carbon isotope analyzer to which the present invention is applied.

FIG. 2 is an infrared absorption spectrum diagram of CO ₂ measured in this example.

FIG. 3 is a block diagram showing an example of a conventional isotope analyzer.

FIG. 4 (a) is an infrared absorption spectrum of ¹² CO ₂ .
(B) is an infrared absorption spectrum of ¹³ CO ₂ .

FIG. 5: CO ₂ measured by a conventional isotope analyzer
FIG. 3 is an infrared absorption spectrum diagram of

[Explanation of symbols]

 1 Semiconductor Laser 2,11 Sample Cell 3,12 Sample Gas Inlet 4,13 Sample Gas Outlet 5,18 Photodetector 6 Lock-in Amplifier 7 Temperature Controller 8 Current Controller 9 Oscillator 10 Lamp 15 Mirror 16 Diffraction Grating 17 slit

Claims (2)

[Claims] 1. A near-infrared semiconductor laser in an isotope analyzer for detecting an isotope ratio of an analyte in which a plurality of carbon isotopes ¹² CO ₂ and ¹³ CO ₂ are mixed based on an optical absorption spectrum intensity ratio. A means for sweeping the oscillation wavelength of the semiconductor laser, a frequency modulating means for frequency-modulating the semiconductor laser, and a laser beam emitted from the semiconductor laser and having passed through an object in which the plurality of carbon isotopes are mixed. And a lock-in amplifier for detecting a match between the modulation frequency obtained by the frequency modulation means and the signal frequency of the laser light detected by the photodetector, and the semiconductor laser Emission wavelength is 6253.7
The optical absorption spectrum of ¹² CO ₂ at 3 ± 0.2 cm ^-1 ,
Similarly, the carbon isotope analyzer is characterized in that the intensity ratio with the optical absorption spectrum of ¹³ CO ₂ when the emission wavelength is 6253.90 cm ⁻¹ is detected. 2. The optical absorption spectrum intensity ratio of ¹² CO ₂ when the emission wavelength of the semiconductor laser is 6254.67 ± 0.2 cm ⁻¹ and the emission wavelength is 625
The intensity ratio to the light absorption spectrum of ¹³ CO ₂ at 5.14 ± 0.2 cm ⁻¹ , the light absorption spectrum of ¹² CO _{2 at} an emission wavelength of 6255.58 ± 0.2 cm ⁻¹ , and the light absorption wavelength of 6255.14 ± 0.2 cm
Intensity ratio with the light absorption spectrum of ¹³ CO ₂ at ^-1 , the light absorption spectrum of ¹² CO ₂ when the emission wavelength is 6257.29 ± 0.2 cm ^-1 , and the emission wavelength is 6257.51 ± 0.2 cm
The intensity ratio with the light absorption spectrum of ¹³ CO ₂ at ^-1 , the light absorption spectrum of ¹² CO _{2 at} the emission wavelength of 6258.88 ± 0.2 cm ^-1 , and the emission wavelength of 6258.64 ± 0.2 cm
The intensity ratio with the light absorption spectrum of ¹³ CO ₂ at ^-1 , the light absorption spectrum of ¹² CO ₂ when the emission wavelength is 6261.01 ± 0.2 cm ^-1 , and the emission wavelength is 6260.80 ± 0.2 cm
The intensity ratio with the light absorption spectrum of ¹³ CO ₂ at ^-1 , the light absorption spectrum of ¹² CO _{2 at} the emission wavelength of 6261.65 ± 0.2 cm ^-1 , and the emission wavelength of wave number 6261.83 ± 0.2 cm
The intensity ratio with the light absorption spectrum of ¹³ CO ₂ at ^-1 and the light absorption spectrum of ¹² CO ₂ when the emission wavelength is 6252.77 ± 0.2 cm ^-1 and the emission wavelength is 6252.63 ± 0.2 cm
The intensity ratio to the light absorption spectrum of ¹³ CO ₂ at ^-1 and the light absorption spectrum of ¹² CO _{2 at} the emission wavelength of 6251.77 ± 0.2 cm ^-1 and the emission wavelength of 6251.32 ± 0.2 cm
The intensity ratio with the light absorption spectrum of ¹³ CO ₂ at ^-1 and the light absorption spectrum of ¹² CO ₂ when the emission wavelength is 6249.67 ± 0.2 cm ^-1 and the emission wavelength is 6249.98 ± 0.2 cm
Intensity ratio between the ¹³ CO ₂ light absorption spectrum when ^-1, the light absorption spectrum of the ¹² CO ₂ when the emission wavelength wavenumber 6,228.69 ± 0.2 cm ^-1, emission wavelength wavenumber 6,228.44 ± 0.2 cm
The intensity ratio with the light absorption spectrum of ¹³ CO ₂ at ^-1 , the light absorption spectrum of ¹² CO ₂ when the emission wavelength is 6231.72 ± 0.2 cm ^-1 , and the light absorption wavelength of 6232.03 ± 0.2 cm
The intensity ratio with the light absorption spectrum of ¹³ CO ₂ at ^-1 , the light absorption spectrum of ¹² CO _{2 at} the emission wavelength of 6233.19 ± 0.2 cm ^-1 , and the emission wavelength of 6233.77 ± 0.2 cm
The intensity ratio with the light absorption spectrum of ¹³ CO ₂ at ^-1 and the light absorption spectrum of ¹² CO _{2 at} the emission wavelength of wave number 6226.35 ± 0.2 cm ^-1 and the emission wavelength of wave number 6226.59 ± 0.2 cm
The intensity ratio with the light absorption spectrum of ¹³ CO ₂ at ^-1 , the light absorption spectrum of ¹² CO _{2 at} the emission wavelength of 6223.13 ± 0.2 cm ^-1 , and the emission wavelength of 6222.79 ± 0.2 cm
_2. The carbon isotope analysis device according to claim 1, wherein the intensity ratio is the intensity ratio with respect to the optical absorption spectrum of ¹³ CO ₂ at ^-1 .