CN107764780B - Method for measuring molecular rotation energy level structure - Google Patents
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- CN107764780B CN107764780B CN201710924543.6A CN201710924543A CN107764780B CN 107764780 B CN107764780 B CN 107764780B CN 201710924543 A CN201710924543 A CN 201710924543A CN 107764780 B CN107764780 B CN 107764780B
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Abstract
The invention discloses a method for measuring a molecular rotation energy level structure. The invention realizes the ionization and detection of molecules based on the conventional molecular ionization spectrum technology, if the molecules on the molecular rotation energy level to be measured are distributed, pulse depletion laser is introduced to transfer the molecules from the ground state rotation state to the excited state rotation state so as to cause the transfer loss of the number of the ground state molecules, and the signal intensity after the ionization of the ground state molecules is recorded when the frequency of the depletion laser is scanned so as to reflect the molecular distribution rotation state structure; if the molecule rotation energy level to be measured has no molecule population, firstly introducing pulse microwave to transfer the molecule population rotation state to the non-population transfer state, then using the scheme of detecting the molecule population rotation state structure by using the deficient laser to couple the deficient laser with the molecule without the population rotation state, or using the deficient laser to couple the molecule with the molecule without the population rotation state, and recording the signal intensity change after the basic state molecule is ionized when scanning the microwave frequency so as to reflect the energy level transition between the molecule population rotation state and the non-population rotation state.
Description
Technical Field
The invention relates to the technical field of detecting molecular energy level structures by ionization spectrum, in particular to a method for measuring molecular rotation energy level structures.
Background
The measurement of molecular energy level has important significance for researching molecular structure constant, energy state control, potential energy curve and dynamic evolution. Molecules are composed of atoms, but their energy level structure is far more complex than the atomic energy level, and include an electron state, a vibrational state, and a rotational state even without taking electron spin and nuclear spin into consideration. Wherein, the vibrational state and the rotational state are energy level structures unique to molecules. In order to measure the energy level structure of molecules, researchers have developed various spectroscopic techniques including laser-induced fluorescence spectroscopy, time-resolved spectroscopy, direct absorption spectroscopy, ionization spectroscopy, and the like. The first two spectral techniques are suitable for acquiring information related to the transition of a molecular excited state to ground state radiation, and the latter two spectral techniques are suitable for measuring the molecular ground state energy level structure. The electronic state channels of the molecule spontaneous radiation are numerous and can not be controlled,since the ground state electronic state of the molecule is the only state in which the molecule exists stably, it is important to detect the energy level structure of the ground state molecule. Direct absorption spectroscopy has the advantage of high resolution, which can reach the MHz level or even higher, but has the disadvantage of low sensitivity, thus requiring greater molecular density and requiring higher molecular transition probability at the upper and lower levels. Detector of ionization spectra can amplify 10 the ion signal6-108The sensitivity of the ionization spectrum is very high, and even the detection of a single ion can be realized. The disadvantage is the low resolution, since the linewidths of the high-energy pulsed lasers selected for the ionizing light are all in the order of at least GHz, some up to tens of GHz. Therefore, the ionization spectrum technology can only distinguish the vibration state of the molecule, and cannot measure the rotating state energy level structure with smaller frequency interval (usually reaching the order of tens of MHz). If the method for measuring the molecular rotation energy level structure, which has the technical sensitivity of molecular ionization spectroscopy and the technical resolution of direct absorption spectroscopy, can be invented, the related application and scientific research based on the molecular rotation energy level structure can be promoted.
Disclosure of Invention
The invention provides a method for measuring a ground state molecular rotation energy level structure while maintaining the sensitivity of an ionization spectrum technology, aiming at solving the problem that the existing ionization spectrum technology cannot measure the molecular rotation energy level structure.
The technical scheme adopted by the invention to solve the problems is as follows:
a method of measuring a molecular rotational energy level structure, comprising the steps of:
(1) detecting molecules which are distributed on a ground state vibration state by using an ionization spectrum technology, and specifically operating as follows: using high-energy pulse laser to excite the molecules in the ground state vibration state to a molecular excited state vibration state, using the same high-energy pulse laser to excite the molecular excited state vibration state to a molecular ionized state again, and then using a microchannel plate detector or a channel electron multiplier to detect the ionized molecules;
(2) applying a laser beam with a line width of MHz magnitude and power of mW magnitude to a molecule of a ground state vibration state by using a semiconductor laser, wherein the acting time is ms magnitude, a light barrier is arranged on a front light path of the semiconductor laser, the acting time of the laser beam is adjusted by adjusting the on and off of the light barrier, and the laser beam is called a depletion laser;
(3) if the molecular rotation energy level to be measured has molecular population, detecting the molecular rotation energy level by adopting a depletion laser, and specifically operating as follows: (a) the frequency of the depletion laser is tuned to enable the depletion laser to resonate in a molecular ground state rotating state and a molecular excited state rotating state, molecules are transferred from the ground state rotating state to the excited state rotating state, and the molecules can quickly and spontaneously radiate to other vibration states of the ground state due to the fact that the energy level life of the excited state molecules is in ns magnitude; (b) the loss laser is turned off, the molecular ions are detected by adopting high-energy pulse laser, the number of molecules generating photoionization is reduced due to transfer loss of the number of ground state molecules coupled by the loss laser, and the reduced number of molecular ion signals reflects the population of the molecules in the corresponding rotating state; (c) scanning the frequency of the depletion laser, and simultaneously recording the signal intensity change after the basic state molecules are ionized, wherein the signal intensity change reflects the molecular population of the up-conversion dynamic state of a certain vibration state of the basic state, and the larger the signal intensity change is, the more the molecular population is;
(4) if the molecular rotation energy level to be measured does not have molecular population, the detection of the molecular rotation energy level is realized by combining microwave transfer and deficient laser, and the specific operation is as follows: (a) firstly, a microwave source is adopted to act pulse microwaves on ground state molecules, the acting time is in the magnitude of ms, the microwave frequency is tuned between the rotation state of the populated molecules and the rotation state of the undiscovered molecules, and the molecules in the rotation state of the populated molecules can be transferred to the rotation state of the undiscovered molecules; (b) then acting a beam of depletion laser, wherein the acting time is in the magnitude of ms, if the frequency of the depletion laser is tuned to the resonance positions of the molecular ground state non-populated rotating state and the molecular excited state rotating state, the number of molecules subjected to photoionization can be reduced after the depletion laser is turned off and the ionization light is turned on; if the frequency of the depletion laser is tuned to the resonance positions of the molecular ground state population rotation state and the molecular excited state rotation state, when the depletion laser is turned off and the ionization light is turned on, the number of molecules subjected to photoionization is reversely increased on the basis of the number reduction caused by the depletion laser in the step (3); (c) scanning the microwave frequency, and simultaneously recording the signal intensity change after the ionization of the ground state molecules, wherein the signal intensity change reflects the energy level transition between the populated rotating state and the unpopulated rotating state on a certain vibration state of the ground state, and the larger the signal intensity change is, the stronger the energy level transition between the populated rotating state and the unpopulated rotating state on the certain vibration state of the ground state is.
By adopting the technical scheme, the invention solves the technical problem that the rotational state energy level structure with smaller frequency interval cannot be measured when the molecular energy level structure is detected by the existing ionization spectrum technology. The invention realizes the ionization and detection of molecules based on the conventional molecular ionization spectrum technology, if the molecules on the molecular rotation energy level to be measured are distributed, pulse depletion laser is introduced to transfer the molecules from the ground state rotation state to the excited state rotation state so as to cause the transfer loss of the number of the ground state molecules, and the signal intensity after the ionization of the ground state molecules is recorded when the frequency of the depletion laser is scanned so as to reflect the molecular distribution rotation state structure; if the molecule rotation energy level to be measured has no molecule population, firstly introducing pulse microwave to transfer the molecule population rotation state to the non-population transfer state, then using the scheme of detecting the molecule population rotation state structure by using the deficient laser to couple the deficient laser with the molecule without the population rotation state, or using the deficient laser to couple the molecule with the molecule without the population rotation state, and recording the signal intensity change after the basic state molecule is ionized when scanning the microwave frequency so as to reflect the energy level transition between the molecule population rotation state and the non-population rotation state. The method not only maintains the sensitivity of the ionization spectrum technology, but also can measure the energy level and the transition intensity of the rotation state of the populated molecules and the rotation state of the unpopulated molecules, and can obtain the complete information of the rotation energy level structure of the ground state molecules.
Drawings
FIG. 1 is a schematic diagram of the molecular energy levels involved in measuring the molecular rotational energy level structure using a deficient laser and a microwave source in accordance with the present invention;
FIG. 2 shows the RbCs molecular ground state X measured by the laser ablation in the embodiment 11Σ+The rotation state population of the vibration state v ═ 0;
FIG. 3 is the present inventionEmbodiment 2 of the invention RbCs molecular ground state X measured by microwave transition1Σ+And the vibration state v is 0 and is in transition of a populated rotation state and an unpopulated rotation state.
Detailed Description
Example 1
Measurement of RbCs molecular ground state X1Σ+And a rotation state population in which the vibration state v is 0.
The specific operation is as follows:
(1) using a high energy pulsed laser with an energy of 1mJ, a diameter of 3mm, and a pulse width of 7ns, will be at X1Σ+The RbCs molecule in the ground state of 0, v, is first excited to 23Π0 +When v is 8 excitation vibration states, the pulse laser excites the molecules of the excitation vibration states to RbCs molecules ionization states again, and then the RbCs molecules of the ionization states are detected through a microchannel plate detector;
(2) preparing a semiconductor laser as a depletion laser, wherein the line width of the laser is 2MHz, the used laser power is 2mW, and an optical switching device is adopted to obtain pulse depletion laser with the action time of 2 ms;
(3) detection of the RbCs molecular ground state X as follows1Σ+And the rotation state population of the vibration state v ═ 0: (a) frequency tuning of the deficit laser to the ground state X1Σ+V ═ 0 vibrational state and excited state 23Π0 +V is 8 around the transition of the vibrational state. (b) And (3) applying 2ms of pulse depletion laser, then opening the high-energy pulse laser to ionize the RbCs molecules and detecting the RbCs molecules by using a microchannel plate. (c) Scanning the deficient laser frequency to obtain the RbCs molecular electronic state X1Σ+And the molecular rolling state population on the vibrational state v ═ 0 as shown in fig. 2. In the figure, the abscissa is the laser frequency of the deficit laser and the ordinate is the normalized RbCs+Molecular ion signal, the solid line is the Lorentzian equation fitted curve. The decrease of the molecular ion signal corresponds to the population of the molecule in the rotation state, and the two peak positions in the diagram correspond to X respectively1Σ+Electronic state v-0 vibrational state up-conversion state J-0 and rotational state J-2 to upper level 23Π0 +Electronic state v ═ 8The transition of the rotation states of J1 and J3 in the vibration state, and the laser frequency difference value is the energy level interval of the two rotation states.
Example 2
Measurement of RbCs molecular ground state X1Σ+And the vibration state v is 0 and is in transition of a populated rotation state and an unpopulated rotation state.
The specific operation is as follows:
(1) using a high energy pulsed laser with an energy of 1mJ, a diameter of 3mm, and a pulse width of 7ns, will be at X1Σ+The RbCs molecule in the ground state of 0, v, is first excited to 23Π0 +When v is 8 excitation vibration states, the pulse laser excites the molecules of the excitation vibration states to RbCs molecules ionization states again, and then the RbCs molecules of the ionization states are detected through a microchannel plate detector;
(2) preparing a semiconductor laser as a depletion laser, wherein the line width of the laser is 2MHz, the used laser power is 2mW, and an optical switching device is adopted to obtain pulse depletion laser with the action time of 2 ms;
(3) measurement of the RbCs molecular ground state X as follows1Σ+Transition of the populated and unpopulated rotating state on the vibrational state v ═ 0: (a) using a microwave source of type SG386 and a microwave switch of type ZFSWA2-63DR +, microwave pulses of action time 2ms and action power 10 μ W are generated, the frequency being tuned around the transitions of rotation state J-1 and rotation state J-2. (b1) Coupling the frequency of the depletion laser to the molecular ground state X1Σ+The non-populated J-2 rotation state of the electronic state v-0 oscillation state to the upper energy level 23Π0 +The electronic state v is 8 and the J is 3. (c1) Scanning microwave frequency, and simultaneously recording signal intensity change after ground state molecule ionization to obtain RbCs molecule ground state X1Σ+The transition between the populated and unpopulated rotated states on the vibrational state v ═ 0, as shown in fig. 3 for the "deficient laser coupled unpopulated state". (b2) Coupling the frequency of the depletion laser to the molecular ground state X1Σ+J-1 rotation state to upper energy level 2 of electronic state v-0 mass in vibrational state3Π0 +J2 turns in the electronic state v 8 vibration stateAnd (4) dynamic state. (c2) Scanning microwave frequency, recording signal intensity change after ground state molecule ionization, and obtaining RbCs molecule ground state X1Σ+The transition between the populated and unpopulated rotated states at vibrational state v ═ 0, as shown in fig. 3 for "the deficient laser coupled populated state". The abscissa of the graph is the microwave frequency and the ordinate is the normalized RbCs+Molecular ion signal, the solid line is the Lorentzian equation fitted curve. The two-minute method is consistent with measurements of the amount of transfer between the rotational states of the molecule and the frequency separation.
Claims (1)
1. A method for measuring a molecular rotation energy level structure is characterized by comprising the following steps:
(1) detecting molecules which are distributed on a ground state vibration state by using an ionization spectrum technology, and specifically operating as follows: using high-energy pulse laser to excite the molecules in the ground state vibration state to a molecular excited state vibration state, using the same high-energy pulse laser to excite the molecular excited state vibration state to a molecular ionized state again, and then using a microchannel plate detector or a channel electron multiplier to detect the ionized molecules;
(2) applying a laser beam with a line width of MHz magnitude and power of mW magnitude to a molecule of a ground state vibration state by using a semiconductor laser, wherein the acting time is ms magnitude, a light barrier is arranged on a front light path of the semiconductor laser, the acting time of the laser beam is adjusted by adjusting the on and off of the light barrier, and the laser beam is called a depletion laser;
(3) if the molecular rotation energy level to be measured has molecular population, detecting the molecular rotation energy level by adopting a depletion laser, and specifically operating as follows: (a) the frequency of the depletion laser is tuned to enable the depletion laser to resonate in a molecular ground state rotating state and a molecular excited state rotating state, molecules are transferred from the ground state rotating state to the excited state rotating state, and the molecules can quickly and spontaneously radiate to other vibration states of the ground state due to the fact that the energy level life of the excited state molecules is in ns magnitude; (b) the loss laser is turned off, the molecular ions are detected by adopting high-energy pulse laser, the number of molecules generating photoionization is reduced due to transfer loss of the number of ground state molecules coupled by the loss laser, and the reduced number of molecular ion signals reflects the population of the molecules in the corresponding rotating state; (c) scanning the frequency of the depletion laser, and simultaneously recording the signal intensity change after the basic state molecules are ionized, wherein the signal intensity change reflects the molecular population of the up-conversion dynamic state of a certain vibration state of the basic state, and the larger the signal intensity change is, the more the molecular population is;
(4) if the molecular rotation energy level to be measured does not have molecular population, the detection of the molecular rotation energy level is realized by combining microwave transfer and deficient laser, and the specific operation is as follows: (a) firstly, a microwave source is adopted to act pulse microwaves on ground state molecules, the acting time is in the magnitude of ms, the microwave frequency is tuned between the rotation state of the populated molecules and the rotation state of the undiscovered molecules, and the molecules in the rotation state of the populated molecules can be transferred to the rotation state of the undiscovered molecules; (b) then acting a beam of depletion laser, wherein the acting time is in the magnitude of ms, if the frequency of the depletion laser is tuned to the resonance positions of the molecular ground state non-populated rotating state and the molecular excited state rotating state, the number of molecules subjected to photoionization can be reduced after the depletion laser is turned off and the ionization light is turned on; if the frequency of the depletion laser is tuned to the resonance positions of the molecular ground state population rotation state and the molecular excited state rotation state, when the depletion laser is turned off and the ionization light is turned on, the number of molecules subjected to photoionization is reversely increased on the basis of the number reduction caused by the depletion laser in the step (3); (c) scanning the microwave frequency, and simultaneously recording the signal intensity change after the ionization of the ground state molecules, wherein the signal intensity change reflects the energy level transition between the populated rotating state and the unpopulated rotating state on a certain vibration state of the ground state, and the larger the signal intensity change is, the stronger the energy level transition between the populated rotating state and the unpopulated rotating state on the certain vibration state of the ground state is.
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| JPS59214737A (en) * | 1983-05-20 | 1984-12-04 | Ishikawajima Harima Heavy Ind Co Ltd | Measuring device for evaluating uniformity of material structure in molecule level |
| WO2011017386A1 (en) * | 2009-08-05 | 2011-02-10 | Blacklight Power, Inc. | Molecular hydrino laser |
| CN203480055U (en) * | 2013-09-23 | 2014-03-12 | 中国科学院武汉物理与数学研究所 | Geopotential third-order derivative measuring transducer based on atom interference effect |
| CN105486676A (en) * | 2015-12-25 | 2016-04-13 | 中国科学院合肥物质科学研究院 | Microwave-assisted laser-induced breakdown spectrum device |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59214737A (en) * | 1983-05-20 | 1984-12-04 | Ishikawajima Harima Heavy Ind Co Ltd | Measuring device for evaluating uniformity of material structure in molecule level |
| WO2011017386A1 (en) * | 2009-08-05 | 2011-02-10 | Blacklight Power, Inc. | Molecular hydrino laser |
| CN203480055U (en) * | 2013-09-23 | 2014-03-12 | 中国科学院武汉物理与数学研究所 | Geopotential third-order derivative measuring transducer based on atom interference effect |
| CN105486676A (en) * | 2015-12-25 | 2016-04-13 | 中国科学院合肥物质科学研究院 | Microwave-assisted laser-induced breakdown spectrum device |
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| Parallel and coupled perpendicular transitions of RbCs 640 nm system: Mass-resolved resonance enhanced two-photon ionization in a cold molecular beam;Lee, Yonghoon等;《JOURNAL OF PHYSICAL CHEMISTRY A》;20080717;第112卷(第31期);7214-7221 * |
| Production and Detection of Ultracold Ground State 85Rb133Cs Molecules in the Lowest Vibrational Level by Short-Range Photoassociation;赵延霆等;《Chinese Physics Letters》;20151130;第32卷(第11期);113301-(1-4) * |
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