JP2017223547A - Multiple reflection cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multiple reflection cell that causes photoreaction of sample gas while preventing the sample gas from coming in contact with reflection surfaces of concave mirrors.SOLUTION: A multiple reflection cell 1 according to the invention includes a container 3 receiving supply of sample gas being an object of photoreaction, and concave mirrors 5 and 7 being housed in the container 3 and arranged so as to face each other. A laser beam is made incident to the container 3, and the incident laser beam is reflected plural times between the concave mirrors 5 and 7 so as to perform the photoreaction. The multiple reflection cell 1 further includes: a shield gas jet nozzle 9 ejecting shield gas for preventing the sample gas from coming in contact with reflection surfaces 5a and 7a of the concave mirrors 5 and 7; and a shield gas supply pipe 11 supplying the shield gas to the shield gas jet nozzle 9.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multi-reflection cell that reflects laser light a plurality of times between a plurality of concave mirrors arranged facing each other, and more particularly to a multi-reflection cell used for photoreaction.

In recent years, a technique for causing a photoreaction by irradiating a gas in a container with laser light having a specific wavelength and inducing an optical transition between specific energy levels has been widely used. For example, Patent Document 1 discloses a technique for concentrating ¹⁸ O by irradiating an ozone molecule ( ¹⁶ O ¹⁶ O ¹⁸ O) containing ¹⁸ O, which is a stable isotope of an oxygen atom, with laser light having a specific frequency (wavelength). Is disclosed.

In the technology that causes such a photoreaction, by increasing the “light utilization” indicating how much laser light is used in the photoreaction, the “energy yield” indicating the result with respect to the input energy is improved.
As a typical method for increasing the “light utilization rate”, there is an increase in the length of the path where the laser beam and the reaction target gas are in contact with each other.
And, as a method of lengthening the optical path, it is possible to simply extend the length of the container in which the reaction is performed along a straight line along the irradiation direction of the laser light, but in this case, the size of the container and the installation space There is a limit from the point of view.
Therefore, a method is generally used in which a plurality of concave mirrors are installed facing each other and laser light is reflected a plurality of times between the concave mirrors to achieve a long optical path. The laser beam reflected between the concave mirrors a predetermined number of times is guided out of the container through the laser transmission window and detected by the detector.

Such a structure in which the concave mirror is arranged to reflect the laser light a plurality of times is generally called a multiple reflection cell.
Patent Document 2 discloses a sample cell in which a plurality of concave mirrors are arranged in a casing and a light beam is multiply reflected between the concave mirrors.

  Usually, since a part of the incident laser light diffuses on the concave mirror surface (reflection surface), the reflection point of the laser light on the reflection surface of the concave mirror becomes a light spot and can be observed with a camera or the like. For this reason, in the multiple reflection cell, a plurality of light spots are observed on the reflection surface of the concave mirror as shown in FIG. 5, and these light spot groups are called spot patterns.

  By checking such a spot pattern, the position and orientation of the concave mirror can be adjusted so that the laser light is reflected a predetermined number of times between the concave mirrors.

Japanese Patent No. 4364529 JP-A-8-35926

  In general, when laser light is reflected by a concave mirror, it is known that a part of the energy of the laser light incident on the reflecting surface of the concave mirror is lost and not reflected. About 25% of this energy loss is converted to heat at the reflecting surface of the concave mirror.

Then, for example, ozone is supplied to the multiple reflection cell as a sample gas, multiple reflection oxygen isotope ¹⁸ ozone molecules using laser light (e.g., ¹⁶ O ¹⁶ O ¹⁸ O) is decomposed by photoreaction O between the concave mirror When the laser beam incident on the reflecting surface of the concave mirror is converted into heat, the ozone molecules contacting the reflecting surface of the concave mirror are decomposed by this heat.

The amount of ozone molecules decomposed by this heat follows the proportion of ozone molecules in the multiple reflection cell, so ¹⁶ O ¹⁶ O ¹⁶ O, which accounts for about 99.8% of the components, decomposes and a large amount of ¹⁶ O ¹⁶ O is produced. Thus, it was a major cause of hindering ¹⁸ O concentration by photoreaction.

  For such a problem, it is considered effective to prevent the sample gas from contacting the reflecting surface of the concave mirror.

  For example, Patent Document 2 does not decompose ozone by photoreaction, but in order to prevent corrosion of the concave mirror due to highly corrosive sample gas, light entering and exiting the housing with the concave mirror is suppressed. There is disclosed a sample cell including a gas container having a portion and configured to isolate the sample gas and the concave mirror by supplying the sample gas to the gas container. However, the sample cell disclosed in Patent Document 2 has a problem that the structure is complicated because the gas container to which the sample gas is supplied is installed in the casing.

  The present invention has been made to solve the above-described problems, and suppresses the reaction of the sample gas on the reflecting surface of the concave mirror by preventing the sample gas from contacting the reflecting surface of the concave mirror. An object of the present invention is to provide a multiple reflection cell that performs photoreaction of a sample gas.

(1) A multiple reflection cell according to the present invention includes a container that receives a supply of a sample gas that is a target of a photoreaction, and a plurality of concave mirrors that are housed in the container and arranged to face each other. A laser beam is incident on the container, and the incident laser beam is reflected between the concave mirrors a plurality of times to cause a photoreaction, and the sample gas is prevented from contacting the reflective surface of the concave mirror. And a shield gas supply pipe for supplying the shield gas to the shield gas injection nozzle.

(2) In the above (1), the shield gas ejection nozzle is installed such that the direction in which the shield gas is ejected can be changed.

(3) In the above (1) or (2), the shield gas is inert to the sample gas.

(4) In any of the above (1) to (3), the sample gas is ozone.

(5) In any of the above (1) to (4), the shield gas is a rare gas, a chlorofluorocarbon gas, or a mixed gas of a rare gas and a chlorofluorocarbon gas.

  In the present invention, a container for receiving a sample gas to be subjected to a photoreaction, and a plurality of concave mirrors accommodated inside the container and arranged to face each other, a laser beam is applied to the container. Incident, the incident laser beam is reflected between the concave mirrors a plurality of times to cause a photoreaction, and a shielding gas is jetted to prevent the sample gas from coming into contact with the reflective surface of the concave mirror By providing a shield gas ejection nozzle and a shield gas supply pipe for supplying the shield gas to the shield gas ejection nozzle, the shield gas can prevent the sample gas from contacting the concave mirror surface, The reaction of the sample gas on the reflecting surface of the concave mirror, particularly the thermal decomposition reaction, can be suppressed.

It is explanatory drawing explaining the outline | summary of the multiple reflection cell which concerns on this Embodiment. It is explanatory drawing explaining the shape and number of shield gas injection nozzles used for the multiple reflection cell which concerns on this Embodiment (the 1). It is explanatory drawing explaining the shape and number of shield gas ejection nozzles used for the multiple reflection cell which concerns on this Embodiment (the 2). It is explanatory drawing explaining the shape and number of shield gas ejection nozzles used for the multiple reflection cell which concerns on this Embodiment (the 3). It is a figure which shows an example of the spot pattern of the laser beam irradiated to the concave mirror of the multiple reflection cell.

  As shown in FIG. 1, a multiple reflection cell 1 according to an embodiment of the present invention includes a container 3 that receives supply of a sample gas that is a target of a photoreaction, and two sheets that are housed and disposed inside the container 3. The concave mirrors 5 and 7, the shield gas jet nozzle 9 for jetting a shield gas for preventing the sample gas from contacting the reflective surfaces 5 a and 7 a of the concave mirrors 5 and 7, and the shield gas jet nozzle 9. A shield gas supply pipe 11 for supplying the shield gas is provided.

  Hereinafter, each configuration of the multiple reflection cell 1 will be described in detail. In addition, in the drawings used in the following description, in order to make the characteristics easy to understand, there are cases where the characteristic portions are enlarged for convenience, but the dimensional ratios of the respective components are the same as the actual ones. Is not limited.

<Concave mirror>
The concave mirrors 5 and 7 have concave reflecting surfaces 5a and 7a, and the reflecting mirrors 5 and 5a reflect the incident laser light a plurality of times on the reflecting surfaces 5a and 5a. Is provided.

In this embodiment, the concave mirrors 5 and 7 are made of synthetic quartz having a diameter of 200 mm and a thickness of 23 mm, and the distance between the concave mirrors is 760 mm. The reflectivity of the concave mirrors 5 and 7 is 99%. However, the present invention is not limited to this, and an arbitrary shape (diameter, thickness, etc.) and distance can be selected.
The number of the concave mirrors 5 and 7 is not limited, and any number can be used as long as the laser beam can be reflected a predetermined number of times.

<Container>
The container 3 is cylindrical and accommodates concave mirrors 5 and 7 inside.
The container 3 is provided with a laser transmission window 15 through which laser light emitted from the laser light source 13 is transmitted, and a guide mirror 17 that reflects the laser light emitted through the laser transmission window 15 toward the concave mirror 7.

  An observation window 19 is installed in the container 3, and the spot pattern of the laser beam on the reflection surface 7 a of the concave mirror 7 can be observed and the spot pattern can be photographed by the camera 21.

  The laser beam reflected a predetermined number of times in the container 3 is incident again on the guide mirror 17 and reflected, and then exits the container 3 through the laser transmission window 15. In the multiple reflection cell 1 shown in FIG. 1, a detector 23 for detecting the laser light emitted from the container 3 is installed.

  Furthermore, the gas introduction pipe 25 and the gas outlet pipe 27 are connected to the container 3, respectively, and the sample gas to be used for the photoreaction is introduced into the container 3 through the gas introduction pipe 25 and undergoes the photoreaction. Is led out through the gas lead-out pipe 27.

  In the present embodiment, the container 3 is a steel pipe made of SUS304 having an outer diameter of 300 mm, a thickness of 4 mm, and a length of 1000 mm. However, the size and material of the container 3 are not limited to this, and are arbitrary. Can be selected.

  The laser transmission window 15 is made of Kovar having a diameter of 34 mm and a thickness of 2 mm, the guide mirror 17 is made of synthetic quartz having a diameter of 5 mm and a reflection angle of 45 degrees, and the observation window 19 is made of Kovar having a diameter of 137 mm and a thickness of 8 mm. Although the thing made from each is used, size and material are not limited to these, It can select arbitrarily.

<Mirror fixing member>
The mirror fixing members 29 and 31 hold the back side of the concave mirrors 5 and 7 and fix them to the container 3.

  The concave mirrors 5 and 7 are installed inside the container 3 with their positions (distance between mirrors) and directions (tilting direction, swinging direction) fixed by mirror fixing members 29 and 31.

More preferably, the mirror fixing members 29 and 31 have a mirror adjustment mechanism that strictly adjusts the position and orientation of the concave mirrors 5 and 7.
In this case, the position and orientation of the concave mirrors 5 and 7 are adjusted by adjusting the position (direction between mirrors and vertical direction) and direction (tilting direction and swinging direction) of the concave mirrors 5 and 7 at normal temperature and normal pressure. It is adjusted by.

<Shield gas ejection nozzle>
The shield gas ejection nozzle 9 ejects (inactive) shield gas that does not react with the sample gas toward the reflecting surfaces 5a and 7a of the concave mirrors 5 and 7, respectively.

  Here, in order to effectively prevent the sample gas from coming into contact with the reflection surfaces 5a and 7a by the shield gas ejected from the shield gas ejection nozzle 9, the shield gas ejection nozzle 9 is installed at the tip of the shield gas supply pipe 11. In doing so, it is desirable that the direction in which the shielding gas is ejected can be adjusted as appropriate so that it can be changed.

  Further, the shape and the number of the shield gas ejection nozzles 9 can be arbitrarily determined as shown in FIGS.

FIG. 2 shows a shield gas ejection nozzle 9 disposed above and below the reflecting surface 5a, as in FIG.
In FIG. 3, the shield gas ejection nozzles 9 are arranged in four directions, up, down, left, and right of the reflecting surface 5a.
In FIG. 4, the annular shield gas ejection nozzle 10 is arranged on the upper and lower sides according to the outer peripheral edge shape of the reflection surface 5 a, and from the inner circumferential surface of the shield gas ejection nozzle 10 to the reflection surface 5 a side. Shield gas is jetted out.
In any case, it is desirable that the shielding gas be ejected substantially parallel to the surface of the concave mirror 5.

  Further, in the present embodiment, stainless steel made of SUS304 is used as the material of the shield gas ejection nozzle 9, but the material of the shield gas ejection nozzle 9 is not limited to this, and reacts to the sample gas or shield gas. Any material can be selected as long as it does not.

<Supply piping>
The shield gas supply pipe 11 is a pipe for supplying shield gas to the shield gas ejection nozzle 9.

In the present embodiment, stainless steel pipe made of SUS304 is used for the shield gas supply pipe 11, but the material of the shield gas supply pipe 11 is not limited to this, and is made of a material that does not react with the sample gas or the shield gas. Any material can be selected as long as it exists.
In addition, a control valve for controlling the flow rate of the shield gas may be provided in the middle of the shield gas supply pipe 11.

Next, a laser light reaction method using the multiple reflection cell 1 according to the present embodiment will be described below with reference to FIG. 1 by taking as an example the case where oxygen isotope ¹⁸ O in ozone gas is concentrated by photoreaction. .

First, the laser light source 13 and the camera 21 are installed outside the container 3. In the present embodiment, a semiconductor laser is used as the laser light source 13. Here, the intensity of the laser beam was 0.3 W, and the wavelength of the laser beam was 988 nm, which decomposes only ¹⁶ O ¹⁶ O ¹⁸ O, which is an isotope component in ozone.

  Next, the mirror fixing members 29 and 31 having a mirror adjusting mechanism are fixed in the container 3 so that the reflecting surface 5a of the concave mirror 5 and the reflecting surface 7a of the concave mirror 7 face each other.

  Then, the positions and orientations of the concave mirrors 5 and 7 are strictly adjusted by the mirror adjusting mechanism of the mirror fixing members 29 and 31. Here, the distance between the concave mirrors is set to 760 mm, and the number of reflections of the laser light between the concave mirrors 5 and 7 at this time is about 160 times.

  Then, laser light is emitted from the laser light source 13 and introduced into the container 3 through the laser transmission window 15.

  The laser light introduced into the container 3 is reflected by the guide mirror 17 toward the concave mirror 7 side. The laser light reflected between the concave mirrors 5 and 7 a predetermined number of times (= about 160 times) is incident on the guide mirror 17 again and reflected toward the laser transmission window 15, and passes through the laser transmission window 15 and is outside the container 3. Exit to.

  The number of reflections of the laser light between the concave mirrors 5 and 7 can be measured by photographing a spot pattern of the laser light irradiated on the reflection surface 7 a of the concave mirror 7 with the camera 21.

  After confirming that the positions and orientations of the concave mirrors 5 and 7 are adjusted by the photographed spot pattern, the emission of the laser light from the laser light source 13 is stopped. Then, after the inside of the container 3 is evacuated by a vacuum pump (not shown) through the gas outlet pipe 27, ozone, which is a photoreaction sample gas, is supplied from the gas introduction pipe 25 into the container 3.

  At the same time, the shield gas is supplied from the shield gas supply pipe 11 and argon gas is ejected from the shield gas ejection nozzle 9 as the shield gas to the reflective surfaces 5a and 7a.

  Finally, by emitting laser light from the laser light source 13 and introducing the laser light into the container 3 through the laser transmission window 15, ozone photoreaction can be performed.

As described above, in the multiple reflection cell 1 according to the present invention, ozone molecules come into contact with the reflection surfaces 5a and 7a of the concave mirrors 5 and 7 by the argon gas ejected in the vicinity of the reflection surfaces 5a and 7a of the concave mirrors 5 and 7. This can be prevented, and the thermal decomposition of ozone molecules on the reflecting surfaces 5a and 7a of the concave mirrors 5 and 7 is suppressed, so that the concentration efficiency of the stable isotope ¹⁸ O can be greatly increased.

  In the above description, the shielding gas is argon gas, which is one of the rare gases that do not react with ozone, which is the sample gas. However, the shielding gas according to the present invention is not limited to this, and other Or a mixed gas of rare gas and Freon gas.

[Concentration effect of oxygen stable isotopes in multiple reflection cells]
When the oxygen isotope ¹⁸ O in the ozone gas is concentrated by the multi-reflection cell 1 according to the present embodiment, the shielding gas is ejected to the reflecting surfaces 5a and 7a side of the concave mirrors 5 and 7, whereby the reflecting surfaces 5a and The concentration effect of ¹⁸ O in the case where generation of oxygen molecules due to thermal decomposition of ozone molecules in 7a is prevented is estimated.

It is known that the enrichment of ¹⁸ O follows the following reaction mechanism when an ozone molecule ( ¹⁶ O ¹⁶ O ¹⁸ O) containing ¹⁸ O, which is a stable isotope of oxygen atom, is irradiated with laser light of a specific frequency. (See Patent Document 2).

First, when laser light is irradiated to ozone molecules O ₃ (for example, ¹⁶ O ¹⁶ O ¹⁸ O), as shown in the formula (1), they are separated into one oxygen molecule and one oxygen atom.
O ₃ + “Laser irradiation” → O ₂ + O (1)

Since the oxygen atom O generated by the reaction of the formula (1) has gained energy, as shown in the formula (2), some of the ozone molecules O ₃ existing around are decomposed.
O + nO ₃ → 0.5 (1 + 3n) O ₂ (2)

In equation (2), n is called the entrainment factor. If n = 5, if one ozone molecule is decomposed by laser light irradiation, five ozone molecules are decomposed according to equation (2). Therefore, the equations (1) and (2) The reaction decomposes a total of six ozone molecules (the natural abundance of ¹⁸ O is about 0.2%, so almost all are ¹⁶ O ¹⁶ O ¹⁶ O), resulting in nine oxygen molecules O ₂ .

At this time, the concentration of ¹⁸ O contained in the generated nine oxygen molecules is about 5.6%, which corresponds to a concentration effect of about 28 times compared with the natural abundance ratio of ¹⁸ O (= about 0.2%).

Next, the amount of ozone molecules decomposed by laser light is estimated.
In the concentration of ¹⁸ O using the multiple reflection cell 1 according to the embodiment of the present invention, the pressure of ozone in the container 3 is −60 kPaG, the temperature is −60 ° C., the laser beam energy is 0.3 W, the wavelength is 992 nm, ^When the natural abundance ratio of ¹⁸ O is 0.2%, and the amount of ozone molecules decomposed by laser light is calculated from these conditions, it is 8.48 × 10 ⁻⁹ [mol / sec].

Here, when the entrainment coefficient in Equation (2) is n = 5, the production amount of oxygen molecules is
8.48 × 10 ^-9 × 9 ＝ 7.63 × 10 ^-8 [mol / sec] (3)
It becomes.

On the other hand, as a comparison object, the concentration effect of ¹⁸ O by a conventional multiple reflection cell in which shield gas was not jetted onto the reflecting surface of the concave mirror was calculated.

If the reflectivity of the concave mirror is 99%, the first reflection of 0.3W laser light,
0.3 × 0.99 = 0.297 [W] (4)
Is reflected,
0.3−0.297 = 0.003 [W] (5)
However, it is a loss at the concave mirror.

Therefore, the total loss when 160 reflections occur between the concave mirrors is
0.3 × (1-0.99 ¹⁶⁰ ) = 0.24 [W] (6)
It becomes. About 25% of the total loss is converted into heat at the reflecting surface of the concave mirror.

Since the energy required to decompose ozone molecules by heat is 101 kJ / mol, the amount of ozone thermally decomposed on the reflecting surface of the concave mirror is
0.24 x 0.25 / (101 x 10 ³ ) = 5.94 x 10 ^-7 [mol / sec] (7)
It becomes.

Furthermore, when the amount of oxygen molecules produced by the thermal decomposition of ozone is determined, in the thermal decomposition reaction, 1.5 oxygen molecules are produced from one ozone molecule.
5.97 × 10 ⁻⁷ × 1.5 = 8.96 × 10 ⁻⁷ [mol / sec] (8)
It becomes.

Therefore, the ¹⁸ O concentration in the case of using the conventional multiple reflection cell is
(0.002 × 8.96 × 10 ⁻⁷ + 0.056 × 7.63 × 10 ⁻⁸ ) / (8.96 × 10 ⁻⁷ + 7.63 × 10 ⁻⁸ ) = 0.0062 = 0.62% (9)
It becomes.

This is a concentration effect that is about three times that of the natural abundance of ¹⁸ O, which is about 0.2%.
That is, when ozone is photoreacted by using the multiple reflection cell 1 according to the present embodiment to concentrate the oxygen isotope ¹⁸ O, the shielding gas is ejected to the reflection surfaces 5a and 7a of the concave mirrors 5 and 7 to generate ozone. It was suggested that by preventing the thermal decomposition of, the enrichment effect of stable isotope ¹⁸ O was obtained 5.6% / 0.62% = about 9 times that in the case of using the conventional multiple reflection cell.

  As described above, according to the multiple reflection cell according to the present invention, when the sample gas is photoreacted, the shield gas is ejected to the reflecting surface side of the concave mirror so that the sample gas contacts the reflecting surface of the concave mirror. By preventing the reaction of the sample gas on the reflecting surface of the concave mirror, particularly the thermal decomposition reaction, the sample gas can be photoreacted effectively.

DESCRIPTION OF SYMBOLS 1 Multiple reflection cell 3 Container 5 Concave mirror 5a Reflective surface 7 Concave mirror 7a Reflective surface 9 Shield gas ejection nozzle 10 Shield gas ejection nozzle 11 Shield gas supply piping 13 Laser light source 15 Laser transmission window 17 Guide mirror 19 Observation window 21 Camera 23 Detection 25 Gas inlet pipe 27 Gas outlet pipe 29 Mirror fixing member 31 Mirror fixing member

Claims (5)

A container that receives supply of a sample gas to be subjected to a photoreaction, and a plurality of concave mirrors that are accommodated inside the container and arranged to face each other. A multi-reflection cell that performs photoreaction by reflecting laser light a plurality of times between the concave mirrors,
A shield gas ejection nozzle that ejects a shield gas that prevents the sample gas from contacting the reflecting surface of the concave mirror;
And a shield gas supply pipe for supplying the shield gas to the shield gas ejection nozzle.   The multiple reflection cell according to claim 1, wherein the shield gas ejection nozzle is installed so that a direction in which the shield gas is ejected can be changed.   3. The multiple reflection cell according to claim 1, wherein the shield gas is inert to the sample gas.   The multiple reflection cell according to any one of claims 1 to 3, wherein the sample gas is ozone.   The multiple reflection cell according to claim 1, wherein the shielding gas is a rare gas, a chlorofluorocarbon gas, or a mixed gas of a rare gas and a chlorofluorocarbon gas.