CN107764780A - A kind of method for measuring molecule rotational energy level structure - Google Patents

Abstract

A kind of method for measuring molecule rotational energy level structure of the present invention.Molecular ionization spectral technique of the present invention based on routine realizes the ionization and detection of molecule, if there is molecule population in the molecule rotational energy level that need to be measured, introduce pulse eclipse of the sun or moon laser and molecule is transferred to excitation state rotating state so that ground state molecule number is there occurs transfer loss by ground state rotating state, scanning records after ground state molecule ionization signal intensity can when losing money in business the frequency of light reflects molecule population rotating state structure；If there is no molecule population in the molecule rotational energy level that need to be measured, first introducing pulse microwave has population rotating state to be transferred to non-population transfer state molecule, reuse the scheme of above-mentioned eclipse of the sun or moon laser acquisition molecule population rotating state structure, the non-population rotating state of laser coupled molecule will be lost money in business, laser coupled molecule population rotating state can also will be lost money in business, the energy level transition between change in signal strength can reflection molecule population rotating state and non-population rotating state after ground state molecule ionization is recorded when scanning microwave frequency.

Description

A Method for Measuring Molecular Rotational Energy Level Structure

technical field

The invention relates to the technical field of ionization spectrum detection molecular energy level structure, in particular to a method for measuring molecular rotational energy level structure.

Background technique

The measurement of molecular energy levels is of great significance to the study of molecular structure constants, energy state manipulation, potential energy curves and dynamic evolution. Molecules are composed of atoms, but their energy level structure is far more complex than that of atomic energy levels. Even without considering the electron spin and nuclear spin, it also includes electronic states, vibrational states, and rotational states. Among them, the vibrational state and the rotational state are the unique energy level structures of 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, and ionization spectroscopy. Among them, the first two spectroscopic techniques are suitable for obtaining information related to the radiative transition from the excited state of molecules to the ground state, and the latter two are suitable for measuring the energy level structure of the molecular ground state. The electronic state channels of molecular spontaneous emission are numerous and uncontrollable, while the ground state electronic state of the molecule is the only and stable state of the molecule, so it is particularly important to detect the energy level structure of the ground state molecule. The advantage of direct absorption spectroscopy is high resolution, which can reach the order of MHz or even higher, but the disadvantage is low sensitivity, so a larger molecular density is required and a stronger molecular transition probability is required for the upper and lower energy levels. The detector of the ionization spectrum can amplify the ion signal by 10 ⁶ -10 ⁸ times, so the sensitivity of the ionization spectrum is very high, and even the detection of a single ion can be realized. Its disadvantage is low resolution, because the linewidth of the high-energy pulsed laser selected for ionizing light has reached at least GHz level, and some have reached more than ten GHz. Therefore, the ionization spectrum technique can only distinguish the vibration states of molecules, and cannot measure the rotational dynamic energy level structures with small frequency intervals (usually on the order of tens of MHz). If a method for measuring molecular rotational energy level structure with both the sensitivity of molecular ionization spectroscopy and the resolution of direct absorption spectroscopy can be invented, it will promote related applications and scientific research based on molecular rotational energy level structure.

Contents of the invention

In order to solve the problem that the existing ionization spectroscopy technology cannot measure the molecular rotation energy level structure, the invention proposes a method that not only maintains the sensitivity of the ionization spectroscopy technology, but also can measure the molecular rotation energy level structure of the ground state.

The technical scheme that the present invention takes for solving the above problems is:

A method for measuring molecular rotational energy level structure, comprising the following steps:

(1) Use ionization spectroscopy to detect the molecules in the ground state vibration state. The specific operation is as follows: use a high-energy pulsed laser to excite the molecules in the ground state vibration state to the molecular excited state vibration state, and use the same The high-energy pulsed laser excites the molecular excited state vibration state to the molecular ionized state again, and then detects the ionized state molecules with a microchannel plate detector or a channel electron multiplier;

(2) Use a semiconductor laser to act on a beam of laser light with a line width in the order of MHz and a power in the order of mW to the molecules in the ground state vibration state, and the action time is in the order of ms, wherein a stop is set on the optical path in front of the semiconductor laser Light plate, by adjusting the opening and closing of the light baffle to adjust the action time of the laser, the laser is called loss laser;

(3) If there are molecular populations on the rotational energy level of the molecule to be measured, use the depletion laser to detect the rotational energy level of the molecule. The specific operation is as follows: (a) tune the frequency of the depletion laser to make it resonate with the molecular ground state rotational state and Molecular excited state transition state, which transfers the molecule from the ground state transition state to the excited state transition state. Since the energy level lifetime of the excited state molecule is on the order of ns, the molecule will soon spontaneously radiate to other vibration states of the ground state; (b) turn off the deficit Laser, high-energy pulsed laser is used to detect molecular ions. Due to the transfer loss of the number of ground-state molecules coupled by depletion light, the number of molecules that undergo photoionization will decrease, and the reduced number of molecular ion signals reflects the corresponding rotation state. (c) scan the frequency of the depletion laser, and record the signal intensity change after ionization of the ground state molecules at the same time. more populated;

(4) If there is no molecular population on the rotational energy level of the molecule to be measured, the detection of the rotational energy level of the molecule is realized by combining microwave transfer and depletion laser. The specific operation is as follows: (a) First, pulse the ground state molecule with a microwave source Microwave, the action time is on the order of ms, so that the microwave frequency is tuned between the rotational state of the populated molecules and the rotational state of the unpopulated molecules, and can transfer the molecules in the rotational state of the populated molecules to the rotational state of the unpopulated molecules; (b) Then act on a beam of depletion laser, and the action time is on the order of ms. If the frequency of the depletion laser is tuned to the resonance position of the molecular ground state unoccupied rotational state and the molecular excited state rotational state, when the depletion laser is turned off and the ionizing light is turned on, photoelectricity occurs. The number of molecules ionized will decrease; if the frequency of the depletion laser is tuned to the resonance position of the molecular ground state population transition state and the molecular excited state transition state, when the depletion laser is turned off and the ionization light is turned on, the number of photoionized molecules will decrease in the step ( 3) On the basis of the reduction of the number caused by the depletion laser, the reverse increase; (c) scanning the microwave frequency, and simultaneously recording the signal intensity change after the ionization of the ground state molecules, the signal intensity change reflects the population rotation state and the undistributed state in a certain vibration state of the ground state. For the energy level transition between the population-transition state, the greater the signal intensity change, the stronger the energy-level transition between the population-transition state and the non-population state in a certain vibration state of the ground state.

The present invention adopts the above-mentioned technical scheme, and solves the technical problem that the current ionization spectroscopy technology cannot measure the rotational kinetic energy level structure with small frequency intervals when detecting the molecular energy level structure. The present invention realizes ionization and detection of molecules based on conventional molecular ionization spectroscopy technology. If there are molecular populations on the rotational energy level of the molecules to be measured, a pulsed depletion laser is introduced to transfer the molecules from the ground state to the excited state, so that the ground state molecules When the number of transfer losses occurs, when scanning the frequency of the loss light, the signal intensity after ionization of the ground state molecules can be recorded to reflect the molecular population and dynamic structure; The population-transition state is transferred to the non-population transition state, and then the above-mentioned depletion laser is used to detect the molecular population-transition dynamic structure, and the depletion laser is coupled to the molecular non-population transition state, and the depletion laser is coupled to the molecular population transition state. , when scanning the microwave frequency, recording the signal intensity change after ionization of the ground state molecules can reflect the energy level transition between the molecular population transition state and the non-population transition state. The method of the invention not only maintains the sensitivity of the ionization spectroscopy technique, but also can measure the energy levels and transition strengths of the rotational dynamics of the populated molecules and the non-populated molecules, and can obtain complete information on the rotational energy level structure of the ground state molecules.

Description of drawings

Fig. 1 is a schematic diagram of molecular energy levels involved in measuring molecular rotational energy level structure by using depletion laser and microwave source in the present invention;

Fig. 2 is the rotational state population of RbCs molecular ground state X ¹ Σ ⁺ and vibrational state v=0 measured by depletion laser in Example 1 of the present invention;

Fig. 3 is the transition of the RbCs molecular ground state X ¹ Σ ⁺ and the vibration state v=0 measured by using the microwave transition in Example 2 of the present invention.

Detailed ways

Example 1

The rotational state population of RbCs molecular ground state X ¹ Σ ⁺ and vibrational state v=0 was measured.

The specific operation is as follows:

(1) Use a high-energy pulsed laser with an energy of 1mJ, a diameter of 3mm, and a pulse width of 7ns to first excite the RbCs molecule in the ground state vibration state of X ¹ Σ ⁺ , v=0 to 2 ³ Π ₀ ⁺ , v=8 Excite the vibrational state, the pulse laser excites the molecules in the excited vibrational state to the RbCs molecular ionization state again, and then detect the ionized RbCs molecules through the microchannel plate detector;

(2) Prepare a semiconductor laser as the depletion laser, the laser line width is 2MHz, the laser power used is 2mW, and the pulse depletion laser with an action time of 2ms is obtained by using an optical switch device;

(3) Probe the population of the rotational state of RbCs molecular ground state X ¹ Σ ⁺ and vibration state v=0 as follows: (a) The frequency of the depletion laser is tuned to the ground state X ¹ Σ ⁺ vibration state of v=0 and the excited state 2 ³ Π ₀ ⁺ near the transition of the v=8 vibrational state. (b) The pulsed depletion laser was applied for 2ms, and then the high-energy pulsed laser was turned on to ionize the RbCs molecules and detected by the microchannel plate. (c) Scan the frequency of the depletion laser to obtain the molecular rotational state population of RbCs molecular electronic state X ¹ Σ ⁺ and vibrational state v=0, as shown in FIG. 2 . The abscissa in the figure is the depletion laser frequency, the ordinate is the normalized RbCs ⁺ molecular ion signal, and the solid line is the Lorentz formula fitting curve. The reduction of the molecular ion signal corresponds to the population of molecules in the rotational state, and the two peak positions in the figure correspond to X ¹ Σ ⁺ electronic state v=0, the vibrational state, the upward rotational state J=0 and the rotational state J=2 to up The energy level 2 ³ Π ₀ ⁺ electronic state v=8 is the transition of the J=1 and J=3 rotational states on the vibrational state, and the laser frequency difference is the energy level interval of these two rotational states.

Example 2

Measure the transitions of the RbCs molecular ground state X ¹ Σ ⁺ and the vibration state v=0 between the population transition state and the non-population transition state.

The specific operation is as follows:

(1) Use a high-energy pulsed laser with an energy of 1mJ, a diameter of 3mm, and a pulse width of 7ns to first excite the RbCs molecule in the ground state vibration state of X ¹ Σ ⁺ , v=0 to 2 ³ Π ₀ ⁺ , v=8 Excite the vibrational state, the pulse laser excites the molecules in the excited vibrational state to the RbCs molecular ionization state again, and then detect the ionized RbCs molecules through the microchannel plate detector;

(2) Prepare a semiconductor laser as the depletion laser, the laser line width is 2MHz, the laser power used is 2mW, and the pulse depletion laser with an action time of 2ms is obtained by using an optical switch device;

(3) Measure RbCs molecular ground state X ¹ Σ ⁺ , vibrational state v=0 on the transition between population and non-population transition states: (a) Use a microwave source of model SG386 and model ZFSWA2-63DR+ The microwave switch generates microwave pulses with an action time of 2 ms and an action power of 10 μW, and the frequency is tuned near the transitions of the rotational state J=1 and the rotational state J=2. (b1) Frequency-coupling the molecular ground state X ¹ Σ ⁺ electronic state v=0 vibrational state of the unpopulated J=2 rotational state of the extinction light to the upper energy level 2 ³ Π ₀ ⁺ electronic state v=8 vibrational state J =3 turn dynamics. (c1) Scan the microwave frequency and record the signal intensity changes after the ionization of the ground state molecules at the same time, and obtain the transition of the RbCs molecular ground state X ¹ Σ ⁺ and the vibration state v=0 between the population transition state and the non-population transition state, as shown in Figure 3 Shown in "Deficited Optically Coupled Unpopulated State". (b2) The frequency-coupled molecular ground state X ¹ Σ ⁺ electronic state v=0 of the deficient light is coupled to the J=1 rotational state populated on the vibrational state of the upper energy level 2 ³ Π ₀ ⁺ the electronic state v=8 on the vibrational state J= 2 turns dynamic. (c2) Scanning the microwave frequency and recording the signal intensity changes after the ionization of the ground state molecules at the same time can also obtain the transitions of the RbCs molecular ground state X ¹ Σ ⁺ and the vibration state v=0 between the population transition state and the non-population transition state, as shown in the figure 3 in the "deficient optical coupling population state" shown. The abscissa in the figure is the microwave frequency, the ordinate is the normalized RbCs ⁺ molecular ion signal, and the solid line is the Lorentz formula fitting curve. The two clock methods are consistent in the measurement of the transfer amount and the frequency interval between molecular rotational states.

Claims (1)

1. A method for measuring molecular rotation energy level structure, characterized in that it comprises the following steps: (1) Use ionization spectroscopy to detect the molecules in the ground state vibration state. The specific operation is as follows: use a high-energy pulsed laser to excite the molecules in the ground state vibration state to the molecular excited state vibration state, and use the same The high-energy pulsed laser excites the molecular excited state vibration state to the molecular ionized state again, and then detects the ionized state molecules with a microchannel plate detector or a channel electron multiplier; (2) Use a semiconductor laser to act on a beam of laser light with a line width in the order of MHz and a power in the order of mW to the molecules in the ground state vibration state, and the action time is in the order of ms, wherein a stop is set on the optical path in front of the semiconductor laser Light plate, by adjusting the opening and closing of the light baffle to adjust the action time of the laser, the laser is called loss laser; (3) If there are molecular populations on the rotational energy level of the molecule to be measured, use the depletion laser to detect the rotational energy level of the molecule. The specific operation is as follows: (a) tune the frequency of the depletion laser to make it resonate with the molecular ground state rotational state and Molecular excited state transition state, which transfers the molecule from the ground state transition state to the excited state transition state. Since the energy level lifetime of the excited state molecule is on the order of ns, the molecule will soon spontaneously radiate to other vibration states of the ground state; (b) turn off the deficit Laser, high-energy pulsed laser is used to detect molecular ions. Due to the transfer loss of the number of ground-state molecules coupled by depletion light, the number of molecules that undergo photoionization will decrease, and the reduced number of molecular ion signals reflects the corresponding rotation state. (c) scan the frequency of the depletion laser, and record the signal intensity change after ionization of the ground state molecules at the same time. more populated; (4) If there is no molecular population on the rotational energy level of the molecule to be measured, the detection of the rotational energy level of the molecule is realized by combining microwave transfer and depletion laser. The specific operation is as follows: (a) First, pulse the ground state molecule with a microwave source Microwave, the action time is on the order of ms, so that the microwave frequency is tuned between the rotational state of the populated molecules and the rotational state of the unpopulated molecules, and can transfer the molecules in the rotational state of the populated molecules to the rotational state of the unpopulated molecules; (b) Then act on a beam of depletion laser, and the action time is on the order of ms. If the frequency of the depletion laser is tuned to the resonance position of the molecular ground state unoccupied rotational state and the molecular excited state rotational state, when the depletion laser is turned off and the ionizing light is turned on, photoelectricity occurs. The number of molecules ionized will decrease; if the frequency of the depletion laser is tuned to the resonance position of the molecular ground state population transition state and the molecular excited state transition state, when the depletion laser is turned off and the ionization light is turned on, the number of photoionized molecules will decrease in the step ( 3) On the basis of the reduction of the number caused by the depletion laser, the reverse increase; (c) scanning the microwave frequency, and simultaneously recording the signal intensity change after the ionization of the ground state molecules, the signal intensity change reflects the population rotation state and the undistributed state in a certain vibration state of the ground state. For the energy level transition between the population-transition state, the greater the signal intensity change, the stronger the energy-level transition between the population-transition state and the non-population state in a certain vibration state of the ground state.