Multicomponent small-molecule gas detection method based on infrared spectroscopy and porous material

Abstract

The application discloses a multi-component small-molecule gas detection method based on infrared spectrum and a porous material, relates to the technical field of gas component detection, and can realize detection of gas molecules with a dipole moment such as CH4, CO, CO2 and the like, and also can realize detection of gas molecules without a dipole moment such as hydrogen isotope gas (H2, HD, D2), O2, N2 and the like. The small-molecule gas enrichment effect of the porous material Cu(I)-MFU-4l can increase the gas density, improve the detection sensitivity, and reduce the demand amount of the infrared spectrum analysis on the gas sample.

Description

Technical Field

[0001] This invention relates to the field of gas composition detection technology, and more specifically to a method for detecting multi-component small molecule gases based on infrared spectroscopy and a porous material technology. Background Technology

[0002] The detection of small molecule gases such as hydrogen isotope gases (H2, HD, D2), O2, N2, CH4, CO, CO2, etc. is widely used in the field of nuclear fusion energy related to hydrogen isotopes, as well as other scientific research and production fields such as environmental monitoring, catalysis, gas separation and purification.

[0003] Conventional analytical testing methods include gas chromatography, mass spectrometry, sensor methods, and spectroscopic methods (infrared spectroscopy, Raman spectroscopy), among others. Existing patents disclose the following technologies: The patent with announcement number CN110694589B and the patent title "A Metal-Organic Framework-Silicon-Based Composite Material and Its Preparation Method and Application" discloses the following: The metal-organic framework-silicon-based composite material provided by this invention is formed by a condensation reaction of a metal-organic framework material containing a π-π conjugated structure and a siloxane-modified silicon-based material. It combines the advantages of both metal-organic framework materials and siloxane-modified silicon-based materials. The metal-organic framework material can enhance the ionization efficiency of the target analyte during MALDI-TOF MS analysis, while the siloxane-modified silicon-based material can promote the desorption efficiency of the target analyte during MALDI-TOF MS analysis. Therefore, it can be well applied to the MALDI-TOF MS detection of small molecule compounds, effectively overcoming the problem of severe background interference in the detection of small molecule compounds by traditional matrix methods, and improving the detection sensitivity.

[0004] The aforementioned patent pertains to mass spectrometry, a method with powerful qualitative analysis capabilities. However, it requires a vacuum pump assembly and other supporting equipment, resulting in drawbacks such as high energy consumption, high cost, and large equipment size.

[0005] Furthermore, gas chromatography requires sending a multi-component gas mixture sample into multiple chromatographic columns in series or parallel under a carrier gas for separation, followed by detection using a detector. While offering high quantitative accuracy, it suffers from drawbacks such as difficulty in separating and detecting hydrogen isotope gas components (H2, HD, D2), poor qualitative capabilities, and long analysis times. In sensor-based methods, whether using a single sensor or a sensor array, it is difficult to distinguish multi-component gas mixtures, making quantitative detection of multi-component gases even more challenging. Spectroscopic methods (infrared spectroscopy, Raman spectroscopy) offer short analysis times, but generally suffer from low detection sensitivity and high sample requirements. Moreover, conventional infrared spectroscopy can only detect gas molecules with dipole moments, such as CH4, CO, and CO2, and struggles to detect gas molecules without dipole moments, such as hydrogen isotope gases (H2, HD, D2), O2, and N2. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problem of how to improve the infrared detection sensitivity of components in multi-component gases. This invention provides a method for detecting multi-component small molecule gases based on infrared spectroscopy and porous materials.

[0007] To achieve the above objectives, the present invention specifically adopts the following technical solution: One aspect of the present invention provides a method for detecting multi-component small molecule gases based on infrared spectroscopy, comprising the following steps: S1. Prepare Cu(I)-MFU-4l sample. Place the Cu(I)-MFU-4l sample into a sealed sample cell and pretreat the Cu(I)-MFU-4l sample. S2. Background curve test: Under vacuum conditions, the spectrum of the pretreated Cu(I)-MFU-4l sample is collected as the background curve. S3. Standard curve plotting: The sealed sample cell is sequentially and quantitatively filled with standard gas containing a single component. The gas filling volume, pressure and temperature are recorded. Then, the spectral test is started. The background curve is subtracted, and a series of spectral signals of the corresponding components are collected. The wavenumber position of the characteristic spectral peak is recorded, and the area of ​​the characteristic spectral peak is integrated to establish the relationship curve between the quantitative parameters of the single component gas filling (filling volume or filling equilibrium pressure) and the area of ​​the characteristic spectral peak, so as to obtain the standard curves of different components. S4. Sample Gas Test Preparation: Cu(I)-MFU-4l Sample State Judgment: Since the Cu(I) site can undergo irreversible adsorption and desorption of CO and is contaminated by some organic gases, the effectiveness of the Cu(I) site activity needs to be judged before the test. The judgment criterion is that after filling with air or N2, the spectrum shows the characteristic peak of N2 adsorption. If not, it is necessary to activate it according to step S1 or replace the Cu(I)-MFU-4l sample. S5. Sample gas test: Under the same filling and test conditions as in step S3, fill the sealed sample cell with the mixed gas sample, record the gas filling volume, pressure and temperature, and then start the spectral test. Subtract the background curve, collect the corresponding spectral signal, record the wavenumber position of the characteristic spectral peak, and integrate the area of ​​each characteristic spectral peak. S6. Qualitative testing: Refer to the wavenumber positions of characteristic peaks when testing a single-component standard gas, analyze the characteristic peaks obtained from the sample gas test spectrum, and thus determine the components contained in the sample gas. S7. Quantitative test: Based on the standard curves of each component obtained in step S3 and the characteristic peak areas of each component in the sample gas test spectrum in step S5, calculate the quantitative parameters of each component (charge volume or charge equilibrium pressure) to obtain the content of each component in the sample gas. S8. Preparation for retesting: After the test, raise the sealed sample cell to room temperature and perform vacuum treatment; after completion, collect the spectrum to confirm whether it contains characteristic spectral peaks of other measured components besides CO. If so, continue vacuum treatment; if not, it means that the gas to be tested has been completely desorbed, and steps S5-S7 can be repeated to carry out the retesting process.

[0008] Specifically, the strong adsorption of inorganic small gas molecules by Cu(I) sites within the pores of Cu(I)-MFU-4l is utilized to increase the aggregation density of inorganic small gas molecules per unit area, thereby improving the sensitivity of spectral detection; 2) When gas molecules without dipole moments, such as hydrogen isotope gases (H2, HD, D2), O2, and N2, are adsorbed on Cu(I) sites on the surface of Cu(I)-MFU-4l, the quadrupole moment and dipole moment of these gas molecules will change due to the strong adsorption of Cu(I) sites, resulting in infrared activity. Thus, infrared spectroscopy can be used for detection, broadening the range of gases that can be detected by infrared spectroscopy.

[0009] In addition, the infrared spectroscopy-based detection method proposed in this scheme can not only detect gas molecules with dipole moments such as CH4, CO, and CO2, but also gas molecules without dipole moments such as hydrogen isotope gases (H2, HD, D2), O2, and N2.

[0010] Furthermore, this invention utilizes the enrichment effect of porous material Cu(I)-MFU-4l on small inorganic gas molecules, which increases gas density, improves detection sensitivity, and reduces the amount of sample required for infrared spectroscopy analysis.

[0011] In one embodiment, if the mixed gas sample contains hydrogen isotope gases (H2, HD, D2), the lower limit of the charging temperature in steps S3 and S5 must be higher than the lowest boiling point temperature of the components in the mixed gas sample, and the upper limit is -143°C. The charging amount of the mixed gas sample must be less than the amount of saturated gas adsorbed at the Cu(I) site in the Cu(I)-MFU-4l sample.

[0012] Specifically, it is mmol / g multiplied by the sample volume m(Cu(I)-MFU-4l). At the specified filling temperature, all component gases (H2, HD, D2, O2, N2, CO) are adsorbed onto the Cu(I) sites in the Cu(I)-MFU-4l sample, and the quantitative parameter is the filling volume.

[0013] In one embodiment, if the mixed gas sample contains CH4 or CO2 gas components, the charging temperature in steps S3 and S5 is lower than room temperature, the charging amount of the mixed gas sample needs to be greater than the saturated gas adsorption amount at the Cu(I) site in the Cu(I)-MFU-4l sample, and the quantitative parameter is the adsorption equilibrium pressure of the charging gas.

[0014] In one embodiment, if the mixed gas sample contains CO, N2, and O2 gas components, the charging temperature and charging amount in steps S3 and S5 are not limited, and the quantitative parameter can be either the charging amount or the adsorption equilibrium pressure of the charging gas.

[0015] In one embodiment, the specific method for loading and pretreatment of the porous material Cu(I)-MFU-4l sample in step S1 is as follows: weigh the Cu(I)-MFU-4l sample and load it into a sealed sample cell. Under vacuum conditions, heat it in situ to 180°C and keep it at that temperature for about 0.5 to 3 hours, and then cool it down to room temperature.

[0016] In one embodiment, in step S1, the porous material Cu(I)-MFU-4l is prepared by a post-synthesis modification method and a thermal decomposition method.

[0017] Another aspect of the present invention provides a porous material Cu(I)-MFU-4l that achieves infrared detection by enhancing the adsorption of inorganic small gas molecules, for use in the aforementioned method for detecting multi-component small molecule gases based on infrared spectroscopy.

[0018] In one embodiment, the porous material Cu(I)-MFU-4l is a metal-organic framework material with Cu(I) sites in its porous structure, belonging to the scorpion-type complex.

[0019] In one embodiment, the metal-organic framework material is constructed from zinc ions [Zn5Cl4]6+ and triazole BTDD2-, forming a structure containing pores with diameters of 11.97 mm and 100 mm respectively. and 18.56 The two types of perforated cubic frame structures, each containing five metal nodes, one of which is located in the central octahedral position, while the remaining four nodes form a "scorpion tail" extending into the hole, forming approximately 9.13 The window.

[0020] Specifically, the porous material Cu(I)-MFU-4l was prepared by post-synthesis modification and thermal decomposition, and the preparation method can be found in existing literature. The synthesis method of porous material Cu(I)-MFU-4l is simple, stable in air, and recyclable.

[0021] The Cu(I) site is located at the "scorpion tail" extending into the pore, and it only bonds to 3 -N bonds on the main framework. The coordination of this site has not reached saturation. Cu(I) sites can strongly adsorb small molecule gases such as H2, HD, D2, O2, N2, and CO through coordination bonds. The molar ratio of the adsorbed gas molecules to the Cu(I) sites is 1:1. The Cu(I) site can interact weakly with CH4 and CO2 through van der Waals interactions, and the molar ratio of the adsorbed gas molecules to the Cu(I) site is >1:1. The order of adsorption strength of small molecule gases by Cu(I) sites is as follows: CO>O2>N2>D2>HD>H2>CH4 / CO2; The adsorption of small molecule gases by Cu(I) sites does not lead to the breaking of molecular bonds within inorganic small molecules; The adsorption of small molecules H2, HD, D2, O2, N2, CH4, and CO2 by Cu(I) sites is a reversible adsorption-desorption process. Adsorption can occur at low temperatures, and the lower the temperature, the lower the adsorption equilibrium pressure. However, at high temperatures (≥ room temperature), all inorganic small molecules H2, HD, D2, O2, N2, CH4, and CO2 can be desorbed. The adsorption of small molecule gas CO at the Cu(I) site is irreversible, and high temperature (≥ room temperature) cannot cause CO to desorb.

[0022] After small molecule gases adsorb onto Cu(I) sites, the wavenumber ranges of the characteristic vibrational peaks are as follows: H2 (~3235 cm⁻¹) -1 HD (2820~2910 cm) -1 D2 (2340~2440 cm) -1 O2 (457~581cm) -1 N2 (~2243 cm) -1 CH4 (~3017 cm) -1 CO2 (~2337 cm)-1 CO (~2086 cm) -1 ).

[0023] The detection of small molecule gases involves the qualitative analysis of one or more component gases (H2, HD, D2, O2, N2, CH4, CO, CO2) or one or more component impurity gases (H2, HD, D2, O2, N2, CH4, CO, CO2) in an inert atmosphere, as well as the quantitative analysis of the content of each component.

[0024] The infrared spectrometer should be equipped with at least a sealed sample cell that can provide a constant temperature environment of -143℃ to 600℃. The sealed gas sample cell includes a platform for placing Cu(I)-MFU-4l samples, an inlet / outlet gas interface / path for evacuating and filling the sample cell cavity, and an optical path for testing samples.

[0025] The inlet and outlet ports need to be connected to an external system or device with gas evacuation and filling functions.

[0026] The beneficial effects of this invention are as follows: 1. The infrared spectroscopy-based detection method proposed in this invention can not only detect gas molecules with dipole moments such as CH4, CO, CO2, etc., but also gas molecules without dipole moments such as hydrogen isotope gases (H2, HD, D2), O2, N2, etc.

[0027] 2. This invention utilizes the enrichment effect of porous material Cu(I)-MFU-4l on small inorganic gas molecules, which increases gas density, improves detection sensitivity, and reduces the amount of sample required for infrared spectroscopy analysis. Attached Figure Description

[0028] Figure 1 This is a unit structure diagram of Cu(I)-MFU-4l of the present invention.

[0029] Figure 2 It is a device for detecting small inorganic gas molecules based on infrared spectroscopy.

[0030] Figure 3 shows the spectra collected after quantitative charging of H2, D2, and HD; Figure 3(a) shows the spectra collected after quantitative charging of H2, Figure 3(b) shows the spectra collected after quantitative charging of D2, and Figure 3(c) shows the spectra collected after quantitative charging of HD.

[0031] Figure 4 shows the working curves of H2, D2, and HD; Figure 4(a) is the working curve of H2, Figure 4(b) is the working curve of D2, and Figure 4(c) is the working curve of HD.

[0032] Figure 5 It is a spectrum collected from a mixture of H2 and D2 in an unknown proportion.

[0033] Figure 6 shows the spectrum and standard working curve collected after quantitative CO charging; Figure 6(a) shows the spectrum collected after quantitative CO charging, and Figure 6(b) shows the standard working curve collected after quantitative CO charging.

[0034] Figure 7 shows the spectrum and standard working curve collected after quantitative N2 filling; Figure 7(a) shows the spectrum collected after quantitative N2 filling, and Figure 7(b) shows the standard working curve collected after quantitative N2 filling.

[0035] Figure 8 shows the spectra and standard working curves collected after quantitative CH4 charging; Figure 8(a) shows the spectra collected after quantitative CH4 charging, and Figure 8(b) shows the standard working curves collected after quantitative CH4 charging. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0037] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0038] Example 1 A device for detecting small inorganic gas molecules such as hydrogen isotopes (H2, HD, D2), O2, N2, CH4, CO, CO2, etc., based on infrared spectroscopy, see [see details]. Figure 2 The spectrometer is an infrared spectrometer, and the detector is an MCD detector (mercury-cadmium-telluride detector) with liquid nitrogen cooling. The detection method is diffuse reflectance infrared spectroscopy.

[0039] Figure 2 This is a device for detecting small inorganic gas molecules based on diffuse reflectance infrared spectroscopy: A is the gas outlet / inlet; B is a K-type thermocouple; C is the sample cell; D is the reflector; E is the transmission window; and F is the quantitative gas filling pipeline.

[0040] The sealed gas sample cell for diffuse reflectance infrared spectroscopy detection provides a constant temperature environment from -196°C to 600°C and includes a gas inlet / outlet (A) and an optical path inlet / outlet (E).

[0041] The sealed gas sample cell is connected to a self-made gas filling system via a gas inlet / outlet (A). This system includes a molecular pump assembly, a gas filling line, and two pressure sensors. The cross-shaped gas filling line (F) is used for quantitative gas filling.

[0042] Example 2 A method for detecting hydrogen isotope gases H2, D2, and HD based on infrared spectroscopy.

[0043] The detection device is described in Example 1.

[0044] Before testing, approximately 20 mg of Cu(I)-MFU-4l sample was placed in a sealed gas sample cell and heated in situ to 180°C under vacuum conditions.

[0045] During testing, the spectrum of the Cu(I)-MFU-4l sample (background curve) under vacuum conditions was used as the background, and spectral signals under different filling conditions were collected.

[0046] Working curve plotting: The charging temperature was -143℃. Single-component hydrogen isotope gases (H2, D2, HD) were sequentially charged into the gas charging pipeline, with the total gas charging amount being less than the saturation adsorption amount. During this charging process, all gases were adsorbed, and the pressure in the reaction chamber approached the vacuum level. The charging amount was used as a quantitative parameter.

[0047] After quantitative injection of H2, D2, and HD, the collected spectra are shown in Figure 3 (Figure 3(a), Figure 3(b), Figure 3(c)).

[0048] The obtained working curves for H2, D2, and HD are shown in Figure 4 (Figure 4(a), Figure 4(b), Figure 4(c)).

[0049] The spectrum collected after charging with a mixture of H2 and D2 in unknown proportions is shown in the figure. Figure 5 .

[0050] right Figure 5 The spectral peaks of H2 and D2 were integrated, and the charge amount was estimated based on the working curve in Figure 3. Then, the concentration ratio of H2 and D2 in the sample gas was calculated, which was 38.9%:61.1%.

[0051] Example 3 A method for CO detection based on infrared spectroscopy.

[0052] The detection device is described in Example 1.

[0053] The filling temperature was room temperature (20°C), and the remaining test conditions and methods were the same as in Example 2.

[0054] At 20°C, CO gas was quantitatively injected into the gas injection line, with the total gas injection amount being less than the saturated adsorption capacity (~45 Pa, ~1.08 mmol / g). The injection amount was used as a quantitative parameter.

[0055] The collected spectra and standard working curves are shown in Figure 6 (Figure 6(a) and Figure 6(b)).

[0056] Example 4 A method for detecting N2 based on infrared spectroscopy.

[0057] The detection device is described in Example 1.

[0058] The filling temperature was room temperature (20°C), and the remaining test conditions and methods were the same as in Example 2.

[0059] At 20℃, N2 gas was quantitatively injected into the gas injection pipeline, with each injection exceeding the saturation adsorption capacity. The equilibrium pressure of gas adsorption after injection was used as the quantitative parameter.

[0060] The collected spectra and standard working curves are shown in Figure 7 (Figure 7(a) and Figure 7(b)).

[0061] Example 5 A method for detecting CH4 based on infrared spectroscopy.

[0062] The detection device is described in Example 1.

[0063] The filling temperature was room temperature (20°C), and the remaining test conditions and methods were the same as in Example 2.

[0064] At 20℃, CH4 gas was injected into the metered gas injection pipeline, with each injection volume exceeding the saturation adsorption capacity. The equilibrium pressure of gas adsorption after injection was used as the metering parameter.

[0065] The collected spectra are shown in Figure 8 (Figure 8(a) and Figure 8(b)).

Claims

1. A method for detecting multi-component small molecule gases based on infrared spectroscopy, characterized in that, Includes the following steps: S1. Prepare Cu(I)-MFU-4l sample. Place the Cu(I)-MFU-4l sample into a sealed sample cell and pretreat the Cu(I)-MFU-4l sample. S2. Background curve test: Under vacuum conditions, the spectrum of the pretreated Cu(I)-MFU-4l sample is collected as the background curve. S3. Standard curve plotting: The sealed sample cell is sequentially and quantitatively filled with standard gas containing a single component. The gas filling volume, pressure and temperature are recorded. Then, the spectral test is started. The background curve is subtracted, a series of spectral signals of the corresponding components are collected, the wavenumber position of the characteristic peak is recorded, and the area of ​​the characteristic peak is integrated to establish the relationship curve between the quantitative parameters of the single component gas filling and the area of ​​the characteristic peak, so as to obtain the standard curves of different components. S4. Sample Gas Test Preparation: Cu(I)-MFU-4l Sample State Judgment: Since the Cu(I) site can undergo irreversible adsorption and desorption of CO and is contaminated by some organic gases, the effectiveness of the Cu(I) site activity needs to be judged before the test. The judgment criterion is that after filling with air or N2, the spectrum shows the characteristic peak of N2 adsorption. If not, it is necessary to activate it according to step S1 or replace the Cu(I)-MFU-4l sample. S5. Sample gas test: Under the same filling and test conditions as in step S3, fill the sealed sample cell with the mixed gas sample, record the gas filling volume, pressure and temperature, and then start the spectral test. Subtract the background curve, collect the corresponding spectral signal, record the wavenumber position of the characteristic spectral peak, and integrate the area of ​​each characteristic spectral peak. S6. Qualitative testing: Refer to the wavenumber positions of characteristic peaks when testing a single-component standard gas, analyze the characteristic peaks obtained from the sample gas test spectrum, and thus determine the components contained in the sample gas. S7. Quantitative testing: Based on the standard curves of each component obtained in step S3 and the characteristic peak areas of each component in the sample gas test spectrum in step S5, calculate the sufficient quantitative parameters of each component to obtain the content of each component in the sample gas. S8. Preparation for retesting: After the test, raise the sealed sample cell to room temperature and perform vacuum treatment; after completion, collect the spectrum to confirm whether it contains characteristic spectral peaks of other measured components besides CO. If so, continue vacuum treatment; if not, it means that the gas to be tested has been completely desorbed, and steps S5-S7 can be repeated to carry out the retesting process.

2. The method for detecting multi-component small molecule gases based on infrared spectroscopy according to claim 1, characterized in that, If the mixed gas sample contains hydrogen isotope gases (H2, HD, D2), the lower limit of the charging temperature in steps S3 and S5 must be higher than the lowest boiling point temperature of the components in the mixed gas sample, and the upper limit is -143℃. The charging amount of the mixed gas sample must be less than the amount of saturated gas adsorbed at the Cu(I) site in the Cu(I)-MFU-4l sample.

3. The method for detecting multi-component small molecule gases based on infrared spectroscopy according to claim 1, characterized in that, If the mixed gas sample contains CH4 or CO2 gas components, the charging temperature in steps S3 and S5 should be lower than room temperature, and the charging amount of the mixed gas sample should be greater than the saturated gas adsorption amount at the Cu(I) site in the Cu(I)-MFU-4l sample. The quantitative parameter is the adsorption equilibrium pressure of the charging gas.

4. The method for detecting multi-component small molecule gases based on infrared spectroscopy according to claim 1, characterized in that, If the mixed gas sample contains CO, N2, and O2 gas components, then the charging temperature and charging amount in steps S3 and S5 are not limited, and the quantitative parameter can be either the charging amount or the adsorption equilibrium pressure of the charging gas.

5. The method for detecting multi-component small molecule gases based on infrared spectroscopy according to claim 1, characterized in that, In step S1, the specific method for loading and pretreatment of the porous material Cu(I)-MFU-4l sample is as follows: Weigh the Cu(I)-MFU-4l sample and load it into a sealed sample cell. Under vacuum conditions, heat it in situ to 180℃ and keep it at that temperature for 0.5~3 h, and then cool it down to room temperature.

6. The method for detecting multi-component small molecule gases based on infrared spectroscopy according to claim 1, characterized in that, In step S1, the porous material Cu(I)-MFU-4l is prepared by post-synthesis modification and thermal decomposition.

7. A porous material Cu(I)-MFU-4l that achieves infrared detection by enhancing the adsorption of small inorganic gas molecules, characterized in that, A method for detecting multi-component small molecule gases based on infrared spectroscopy, as described in any one of claims 1 to 6.

8. The porous material Cu(I)-MFU-4l for infrared detection by enhancing the adsorption of small inorganic gas molecules according to claim 7, characterized in that, Porous material Cu(I)-MFU-4l is a metal-organic framework material with Cu(I) sites in its porous structure, belonging to scorpion-type complexes.

9. The porous material Cu(I)-MFU-4l for infrared detection by enhancing the adsorption of small inorganic gas molecules according to claim 8, characterized in that, The structure of the metal-organic framework material is constructed from zinc ions [Zn5Cl4]6+ and triazole BTDD2-, forming a structure containing pores with diameters of 11.97 mm and 100 mm respectively. and 18.56 The two types of perforated cubic frame structures, each structural unit containing 5 metal nodes, one of which is located in the central octahedral position, and the remaining 4 nodes form a "scorpion tail" extending into the hole, forming a 9.13 The window.

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