EP0571622A1

EP0571622A1 - Sequential observation method for monitoring the evolution of a chemical reaction.

Info

Publication number: EP0571622A1
Application number: EP93902336A
Authority: EP
Inventors: Fernand Marcel Devienne
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-12-17
Filing date: 1992-12-16
Publication date: 1993-12-01
Anticipated expiration: 2012-12-16
Also published as: FR2685086B1; EP0571622B1; DE69210015D1; FR2685086A1; WO1993012535A1; DE69210015T2; US5374559A

Abstract

Procédé d'observation séquentielle des états successifs d'une réaction chimique en cours de déroulement dans un vide élevé ou sous une faible pression ou détermination de la nature d'un corps ou de la composition d'un mélange pouvant être liquide, solide ou gaazeux; ou d'aérosols contenus dans l'air, cela par dissociation dans une boîte de collision (20) remplie d'un gaz neutre, des molécules des composés formés, puis filtration en énergie des fragments de dissociation dans un analyseur électrostatique (22) et détection (24), caractérisé en ce que les molécules des composés à analyser sont formées sur une cible (4) dont les parois conductrices sont portées à une haute tension électrique continue, la cible (4) étant bombardée par deux canons moléculaires fournissant des jets moléculaires neutres d'énergie élevée (ou des mélanges d'ions et de neutres ou simplement des ions), à savoir un premier jet continu (16) apportant des atomes et molécules destinés à réagir ensemble et/ou avec la cible, et un second jet intermittent (18) de molécules de gaz neutre destiné à ioniser, par choc, les molécules formées. Le dispositif est tel que, dans la plupart des cas, les faisceaux de neutres et d'ions secondaires sont dans un même plan vertical.Method for sequential observation of the successive states of a chemical reaction during a high vacuum or under low pressure or determination of the nature of a body or of the composition of a mixture which may be liquid, solid or gaseous ; or aerosols contained in the air, this by dissociation in a collision box (20) filled with a neutral gas, molecules of the compounds formed, then energy filtration of the dissociation fragments in an electrostatic analyzer (22) and detection (24), characterized in that the molecules of the compounds to be analyzed are formed on a target (4) whose conductive walls are brought to a high continuous electrical voltage, the target (4) being bombarded by two molecular cannons providing jets high-energy neutral molecules (or mixtures of ions and neutrals or simply ions), namely a first continuous jet (16) bringing atoms and molecules intended to react together and / or with the target, and a second intermittent jet (18) of neutral gas molecules intended to ionize, by shock, the molecules formed. The device is such that, in most cases, the beams of neutrals and secondary ions are in the same vertical plane.

Description

PROCESS FOR _3EQUEOTIEl_LE OBSERVATION OF SUCCESSIVE STATES OF A CHEMICAL REACTION

The main object of the present invention is a method of sequential observation of the successive states of a chemical reaction in progress in vacuum or at low pressure and also the analysis of solids, liquids, gases (under certain conditions) and aerosols.

The study of chemical reactions between various compounds in a fairly high vacuum is useful, for example to reconstruct the stages of formation from simple elements of organic or biological compounds. These reactions generally take place quickly and it is necessary, in order to be able to follow these syntheses, to have an apparatus which makes it possible to study, in real time, the phenomena of formation of organic compounds, in particular those which serve as the basis for living matter.

The present invention specifically relates to a process for observing successive states of a chemical reaction during the course of a vacuum which meets the stated needs.

The process which is the subject of the invention uses known techniques for dissociation of molecular ions by impact on neutral gas molecules and for consecutive identification of the secondary dis¬ sociation ions formed during the reaction. As such, it is largely inspired by the methods described in documents FR-A-2, 622, 699 and FR-A-2, 655,149, at least as regards the analytical phase of the process using a dissociation box filled with a neutral gas, from which secondary ions filtered into energy emerge in an electrostatic analyzer, the level of filtration of which is adjustable. The method of sequential observation of the successive states of a chemical reaction in progress in a vacuum by dissociation in a dissociation box filled with a neutral gas, molecules of the compounds formed, then filtration into energy of the frag- dissociation elements in an electrostatic and detection analyzer, is characterized in that the molecules of the compounds to be analyzed are formed on a target situated in an enclosure whose conducting walls are brought to a high continuous electrical voltage; the target being bombarded by two sources of high-energy neutral molecular jets, namely: a first continuous jet bringing the atoms and molecules intended to react together and / or with the target, and a second intermittent jet of molecules of neutral gas intended ionizing, by shock, the molecules formed; a system of extraction lenses being provided for extracting the ions formed and leading them to the inlet of the dissociation box, each intervention of the second jet thus making it possible to form, each time, an image of the state of the reaction.

The originality of the process, object of the invention, resides in the simultaneous use of two high-energy neutral molecular jets and in the fact that the axes of these jets are located during the implementation of the process in the same vertical plane. This latter arrangement, which is preferable although not compulsory, allows in particular to work on liquids or powders contained in a small horizontal container. The first brings continuously, into the vacuum enclosure in which the target provided for this purpose is placed, the atoms and molecules of which we want to study precisely the chemical reaction in vacuum. The second intermittent molecular stream is a stream of neutral gas molecules, for example -. argon, krypton, xenon whose energy is such that it causes the molecules in situ and immediate ionization as soon as they are formed and which, by sputtering, makes it possible to form a beam of secondary ions. The dissociation occurs only later in the dissociation box provided for this purpose, at the exit of which the secondary ionic fragments formed are identified by their energy using the electrostatic analyzer.

While the first jet, which can be described as "chemical", operates continuously by bringing the atoms and molecules compounds that one wishes to react together, and / or with the target, the second jet is intermittent and it is it which allows, in a way, to photograph the instantaneous state of evolution of the chemical reaction in progress. Indeed, with each intervention of this second intermittent jet, chemical molecules which have just been formed are ionized then immediately extracted from the reaction chamber, dis¬ associated in the dissociation chamber and analyzed by the detector analyzer system. . Precise estimates make it possible to affirm that between the ionization of a molecule and the detection and identification of the secondary ions formed, a time elapses which does not exceed a few microseconds, the ions being, in fact, extracted at energies between 1,000 and 15,000 eV. As it is from the observation of the different secondary fragments detected that we can identify the chemical molecule which had formed in the enclosure just before being ionized, we see that the process thus achieves, with each intervention of the second molecular jet of neutral gas, a true photograph of the state of the chemical reaction in progress and of the appearance of the various compounds which it generates. This second molecular jet can also intervene se¬ rf

Ion any time program desired in advance, namely, for example, an intervention at a chosen time t or several successive interventions at equally chosen times, or even in pulsed form at a constant frequency. Currently, for example, the method can operate with a second pulsed jet, the

-9 period can vary from 10 seconds to a few hundred seconds when necessary. Of course, the implementation of the process requires very precise programming and control by computer of the times of intervention of this second jet rπolécu- laire.

According to a characteristic of the process which is the subject of the invention, the molecular jets commonly have an energy of 0.5 to 15 keV and the vacuum enclosure is brought to a potential of a few thousand volts, for example from 1000 to 15,000 V.

In addition, the vacuum chamber is placed at the pressure desired by the experimenter for the precise study of a determined reaction, but, more often than not, when one wishes to simulate reactions liable to occur. unroll, for example in the interstellar space, this enclosure is brought to a very high vacuum, of the order of 10 ^" to

_9 10 torr. It is also possible to have a higher limit vacuum by using two turbo-molecular pumps in series.

Finally, to simulate as closely as possible the conditions which may be those of reactions taking place in space, it may be interesting to reconstitute in the reaction chamber other parameters than the vacuum and to submit it ci for example, either at a determined temperature, or to ionizing radiation of a certain intensity. Incidentally, it is also possible to facilitate the ionization of heavy molecules (for example proteins), by bombardment with a nitrogen laser providing a ray of wavelength 337 nm. The choice of the nature and the value of the different parameters is, of course, left to the appreciation of the skilled person and is not directly part of the "present invention.

In any case, the invention will be better understood by referring to the description which follows of the apparatus used and of some examples of implementation, a description which will be given by way of illustration and without limitation with reference to FIGS. 1 to 3 attached on the- which:

- Figure 1 shows, very schematically, a device allows¬ both the implementation of the method object of the invention.

- Figure 2 shows the decomposition scheme with the ddiissssoocciiaattiioonn sseeccoonnddaire fragments of cytosine C H ON. obtained by synthesis in a vacuum.

- Figure 3 shows the decomposition scheme, in the form of dissociation fragments, of the phosphocytosine C.H-O.N.P.

46 4 3

In Figure 1, there is shown the vacuum enclosure 2 inside which is implemented the method, object of the invention. It is a simple diagram because the enclosure is much more complicated so that the molecular canons in particular, can feel the desired inclination relative to the vertical axis of the body of the device so as to have the same impact zone of the two molecular jets on the target. In this vacuum enclosure which can reach, for example, a volume of 30 to 30 liters maximum, a high vacuum is maintained, using a primary pump and a turbo-molecular pump, possibly up to at 10 ~ ⁹ torr (this, without the molecular canons working) and, in principle, between 10 ~ ⁷ and 10 " ⁸ torr when everything works.

In this enclosure, the following different devices are located: the target holder (4) -which can be a small bin whose largest dimension does not exceed 20 mm- which can contain either a liquid, a solid powder or en bloc (the target carrier being different in the case of gases or aerosols). Of course, the following will be designated by "target", the body actually touched by the simultaneous imprint of the two beams. The target holder is included in a conductive enclosure (6) -in principle a por¬ tion of vertical cylinder pierced with holes- carried at high voltage _n , this enclosure comprising in particular five orifices, namely: the orifices 8 and 10 for the introduction of jets molecular, 8bis for a direct vision system of the target qrthrough a system of optical lenses, lObis for the introduction of a laser beam and the orifice 12 for the extraction of the molecular ions formed on the target 4. This extraction is carried out using a system of lenses (14, 14a, 14b, 14c, 14d) brought to different potentials, the last 14d being at zero potential.

Two sources of molecular jets (16) and (18) are necessary for the implementation of the method. The source (16), or first jet, sends on the target (4), through the orifice 8, atoms and molecules of compounds whose reaction in vacuum is to be studied.

The second molecular jet (18) introduced through the orifice (10), into the enclosure (6), on the target (4), a jet of neutral molecules obtained by charge exchange, of an inert gas such as, for example, ar¬ gon, krypton or xenon. As already explained previously, the purpose of this second molecular jet (18) is to ionize in situ, as soon as they are formed on the target (4), the molecules originating from the chemical reaction of the compounds introduced by the first molecular jet (16) between them or with the target and subject them to the sputtering effect. The target (4), in fact, can be either foreign to the chemical reaction studied, or, on the contrary, participate in it as it is the case, for example, when it is made of carbon which can react with atoms and molecules of the molecular stream (16). As soon as they are ionized by the jet (18), the molecules formed on the target (4) by chemical reaction are extracted by sputtering and thanks to the electrostatic pins (14) along the path shown diagrammatically by the arrow "F" and they enter a dissociation box (20) filled with a neutral gas where they partially burst into different fragments of secondary ions. According to the theory already developed in the prior documents FR-A-2,622,699 and FR-A-2,655,149, the process of dissociation of the primary ions from the target (4) by impact on the molecules of neutral gas contained in the box dissociation (20) is as follows: a primary ion of mass M and unit charge e leaves the enclosure (6) with the energy ev \. , V _n being the high voltage to which the enclosure (6) is brought. When it is dissociated in the dissociation box (20) into different secondary ions of mass m., Naked, ΠL, each of the secondary ions thus formed takes with it a share of the total energy of the ion M incident, equal to eV-.m / M, and eV _Q .m ₂ / M and eV-.rrt / M, values which we will denote by eV ". At the exit of the dissociation box (20), these secondary ions arrive in the electrostatic analyzer (22) whose filtration energy is eV ". By varying the value V "previous, it is therefore possible to adjust the electrostatic analyzer to a single energy value of the ions which can pass through it. By thus varying V", the energy level of the filtration is scanned. the electrostatic analyzer (22) and one selects, succes¬ sively, the different secondary ions of masses m .., m _... m,, the ion of mass m. through the electrostatic analyzer when eV "= eV.m. / M, or V" / V _Q = rr / M. At the end of the journey, the secondary ions leaving the electrostatic analyzer (22) enter a detector (24) which allows, possibly, their identification. As the diagram for the decomposition of the chemical molecules formed in the enclosure (6) is known in advance, the presence of a sufficient number of these secondary dissociation fragments makes it possible to affirm that the primary molecule, of mass M, was present on the target (4) at the moment when the molecular jet (18) entered into action. It is therefore possible, therefore, to follow, almost instantaneously, the formation of molecules of mass M on the target (4) of the enclosure (6). We will now describe the study of the formation of two important organic molecules as components of ribonucleic and deoxyribonucleic acids and therefore of all living matter. This body is formed by bombarding pure graphite with a mixture of molecular jets of nitrogen, hydrogen and oxygen.

Referring to Figure 2, we describe the case of the cytosine molecule of general formula C.H_ON_ and whose structural formula is:

In the diagram of FIG. 2, the mass peak M = 111 corresponding to the cytosine and various dissociation fragments of this molecule which are characteristic of the latter is shown.

We thus see the molecular peaks of mass 95 corresponding to the formula:

The molecular peak 83 corresponding to the formula

and different mass peaks 69, 68, 67, 66, 56, 55, 52, 40, 29 and 27. The detection, using the apparatus of FIG. 1, of a large number of these secondary peaks, makes it possible to affirm that the cytosine molecule was present in the enclosure (6) at the time of the intervention of the molecular jet (18). For all practical purposes, it will be noted that the molecular weights indicated sometimes differ by one or a few units of the mass corresponding to the chemical formula, this due to the departure of a proton or even a group of atoms .

FIG. 3 shows a diagram of decomposition into secondary fragments of the same nature, but relating to the phosphocytosine of general formula C.LO N.P and of structural formula:

This body was obtained under the same conditions as above but with approximately 1 microgram of pure phosphoric acid PO-H. which was added to the graphite tablet before the experiment using a special device.

Furthermore, the purity of graphite is confirmed if, before adding phosphoric acid, it leaves the apparatus, using only the molecular barrel (18), only carbon ions and

14 ions corresponding to the different carbon clusters up to C for example.

In accordance with what has been explained previously, the formation of phosphocytosine by the apparatus of FIG. 1 is studied there, while monitoring the appearance of peaks of dissociation of secondary mass 175, 173, 150, 148, 127 and 121 which necessarily result from a dissociation of phosphocytosine since they are in the order of the masses of FIG. 3 upstream of the mass 111 of the cytosine. If, as always, V. designates the high voltage to which the enclosure (6) is brought, one must thus search, by the filtration apparatus comprising the analyzer (22) and the detector (24), for the energies eV. 175/191, eV .173 / 191, eV .150 / 191, etc. As soon as these energies are detected in the electrostatic analyzer, it can be said that a primary molecule of phosphocytosine had formed in the 'enclosure (4) at the time of the arrival of the molecular jet (10).

Another example of implementation of the process which is the subject of the invention relates, for example, to the study of the oxidation of a metal. Using the apparatus of FIG. 1, a molecular jet of oxygen is sent using the jet (16) to a metal target whose oxidation is to be studied. It is possible to use a thermal molecular jet provided in this case. The compounds formed, including the metal clusters, can thus be analyzed by dissociation. If we call X a bivalent metal whose primary ions in oxidized form can be, for example: XO, XO, ₂ ° ₂ ' ^X 3 ° 3' ^etc _'" " ^we study the form- mation of secondary compounds for example in X-. and we search for raa ddeess mmaasssseess mm cdont the ratio m / M is equal to the values X./XO, X ₃ 0 / XO etc ..

In the particular case of tantalum which was studied in our laboratory ten years ago, we obtain, for example, with the Ta cluster. : Ta.O, with an oxygen pressure 1.5 10 ~ torr which dissociates as follows: Ta.O., Ta.O-, Ta.O ", Ta ₄ 0, which gives the mass ratios, that is to say of filtered energies: 0.979; 0.959; 0.939 and 0.919

We can follow, thanks to the device, the formation of these oxides by filtering the energy for a determined ratio.

Claims

1 - Method for sequential observation of the successive states of a chemical reaction in progress in a high vacuum or under a low pressure, this by dissociation in a collision box (20) filled with a neutral gas, molecules of formed compounds, then energy filtration of the dissociation fragments in an electrostatic analyzer (22) and detection (24), characterized in that the molecules of the compounds to be analyzed are formed on a target (4), located in a more or less high vacuum enclosure (6), the conductive walls of which are brought to a continuous high electrical voltage, the target (4) being bombarded by two sources of neutral high-energy molecular jets, obtained by charge exchange , namely: a first continuous jet (16) bringing the atoms and molecules intended to react together or with the target and a second intermittent jet (18) of neutral gas molecules intended to ionize, by shock, the molecules formed; an extraction lens system (14) being provided for extracting the secondary ions formed and leading them to the inlet of the dissociation box (20), each intervention of the second jet (18) thus making it possible to form , each time, a picture of the state of the reaction.

2 - Analysis method according to claim 1, characterized in that to analyze liquids, solids, powders, gases, aerosols, the target being contained in target holders horizon¬ rate of variable shape depending on the nature of the bodies to be analyzed, the molecular jets and the secondary ion beam are in the same vertical plane and adjustable in inclination in this plane.

- Analysis method according to Claim 1, characterized in that the molecular jets have an energy of 0.5 to 15 keV and in that the vacuum enclosure (6) is brought to a potential from 1,000 to 15,000 volts.

- Analysis method according to Claim 1, characterized in that the second intermittent molecular jet is a jet pulsed at an adjustable frequency.

- Analysis method according to Claim 1, characterized in that the vacuum enclosure (2, 6) is placed under a vacuum of the order of 10 to 10 ^" torr.

- Analysis method according to Claim 1, characterized in that the ionization can be carried out for very high masses by a pulsed laser (ibis), the extraction being always carried out by the molecular gas cannon (16) .