JP3082450B2 - Jet spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a supersonic molecular jet spectrometer for intermittently jetting a gas containing a sample as a supersonic jet into a vacuum and transmitting the measurement light to measure the absorption.

[0002]

2. Description of the Related Art Absorption / fluorescence analysis in the ultraviolet and visible regions is widely used for analyzing organic compounds. Conventionally, spectra are measured at room temperature, so even if measurements are made in a gaseous state that has no interaction with solvent molecules, the effects of molecular vibration and rotation are added to the electron transition, so the peak width is wide. Become. For this reason, conventionally, the absorption spectrum cannot be qualitatively analyzed based on its fine structure, and is mainly used only for quantitative analysis.

[0003] On the other hand, supersonic molecular jet spectroscopy in which sample molecules are ejected from pores into a vacuum and cooled to near zero degrees for analysis is under study. Since supersonic molecular jet spectroscopy provides a sharp spectrum, qualitative analysis of sample molecules based on microstructure can be performed. FIG.
Is a schematic representation of conventional laser supersonic jet spectroscopy. In the sample chamber 4, a gas containing the sample is intermittently ejected from the nozzle 6 as a supersonic jet. A part of the laser light from the laser device 2 is detected by the half mirror 8 as reference light in the photocell 10, and the laser light transmitted through the half mirror 8 enters the sample chamber 4 and crosses the supersonic jet, and the transmitted light is Photocell 12 as measurement light
Is detected by The ratio is calculated by the ratio calculator 14 from the detection intensities of the reference light and the measurement light, and the absorbance is calculated from the result according to Lambert-Beer's law.

[0004]

In the laser supersonic jet spectroscopy, since a laser device is used, the device becomes large and expensive. SUMMARY OF THE INVENTION It is an object of the present invention to provide a jet spectrometer capable of obtaining a spectral absorption spectrum in a low temperature state by a simple and inexpensive device.

[0005]

SUMMARY OF THE INVENTION A jet spectrometer according to the present invention comprises a sample chamber for intermittently jetting a gas containing a sample as a supersonic jet into a vacuum; A light source for irradiating the jet, a light receiving optical system for dispersing light passing through the sample chamber and simultaneously detecting multiple wavelengths,
A detection signal from the light receiving optical system when a jet is generated in the sample chamber is used as a measurement signal, and a detection signal from the light receiving optical system when a jet is not generated in the sample chamber is used as a reference signal for the same sample. And a signal processing unit for calculating the absorbance from both detection values by repeatedly taking and averaging them. As a light source, there is a xenon lamp that emits white light. A xenon lamp may emit light in synchronism with the jet of the supersonic jet in the sample chamber, or a xenon lamp that emits light continuously may be intermittently synchronized with the jet jet by a mechanical chopper and guided to the sample chamber. Good. An example of a light receiving optical system that detects multiple wavelengths simultaneously is
This is a combination of a polychromator and a diode array detector arranged in a detection section.

[0006]

Both the measurement signal and the reference signal are light that has passed through the sample chamber. The measurement signal is for when a jet is being generated, and the reference signal is for when no jet is being generated. Light absorption measures the degree of light absorption (absorbance) given by the Lambert-Beer law with respect to wavelength. However, since it is a measure of the decrease in light intensity of the light source, the stability of the light source is maintained or slight fluctuations are observed. Monitoring and strict correction are important points in measuring minute absorption, that is, absorption with high sensitivity. In the present invention, a number of measurements are repeatedly performed on the same sample, and statistical noise is reduced by integrating and averaging the measurement signal and the reference signal.

[0007]

FIG. 1 shows an embodiment. The sample chamber 20 is evacuated, and a sample is ejected from the nozzle 22 into the sample chamber 20 as a supersonic jet. The sample is put into a sample reservoir 24 and pushed out into a sample chamber 20 by a carrier gas 26 such as argon. The nozzle 22 has an on-off valve,
Interface 30 from personal computer 28
The opening / closing operation is controlled by a nozzle trigger pulse c provided through the control unit. Jet 23 is provided on the wall of sample chamber 20.
Light from the xenon lamp 32 as a light source
A window leading through 4 is provided. Xenon lamp 3
2 is controlled by the lamp power supply 36 to be turned on intermittently. The lamp power supply 36 is supplied with a lamp trigger pulse d given from the personal computer 28 via the interface 30.

The sample chamber 20 is provided with a window 38 on the emission side opposite to the window on the entrance side in order to take out the light passing through the sample chamber 20 to the outside. A spectroscope 40 is provided close to the sample chamber 20 to split the light from the window 38.
In the spectroscope 40, a diffraction grating 42, an incident-side concave mirror 43, and an outgoing-side concave mirror 44 are provided, and a 512-channel photodiode array sensor 46 for simultaneously receiving the dispersed light over multiple wavelengths is provided. The detection signal of the array sensor 46 passes through the amplifier 47 to the interface 3.
0, is converted into a digital signal, and is taken into the personal computer 28 for signal processing.

Next, the operation of this embodiment will be described with reference to the timing chart of FIG. The personal computer 28 outputs an exposure timing signal a, and sets an interval for acquiring a detection signal from the array sensor 46 in 20 milliseconds or more. As an example, a case where the exposure timing is set to 40 milliseconds will be described as an example. In order to further capture the measuring light M and the reference light R from the personal computer 28 every 120 milliseconds, the personal computer 2
8 outputs a measurement timing signal b to the array sensor 46 via the interface 30. During the period of 40 milliseconds out of 120 milliseconds of the photometric timing, the array sensor 46 can receive light only during the period, and the array sensor 46
Signal is rejected even if light is incident on. As a result, the dark current is reduced.

A nozzle trigger pulse c is generated corresponding to the rising timing of the photometric timing signal b, and the nozzle 22 is opened for about 1 millisecond. Nozzle trigger pulse c
Occurs, a lamp trigger signal d is generated with a delay of about 1 millisecond, and the xenon lamp 32 is turned on. At this time, the jet 23 is on the optical path, light absorption occurs, and a measurement signal M is obtained. Even if the nozzle 22 is not on,
A ramp trigger pulse d is generated based on the rise of the photometric timing signal b, and the reference signal R is captured. The measurement signal M and the reference signal R are detected by the array sensor 46 over multiple channels (multiple wavelengths), taken into the personal computer 28 via the interface 30, and subjected to integration and averaging processing to calculate transmittance or absorbance. Is displayed.

In this embodiment, FIG. 3 shows the result of repeatedly taking in the measurement signal and the reference signal over a plurality of wavelengths and averaging them. The noise level decreases as the number of repetitions increases to 5, 50, and 500 times. The light source fluctuates by about 1% in 10 measurements and decreases in proportion to the square. Therefore, it is equivalent to 0.1% for 1000 times and 0.01% (0.04 mm absorbance (mAbs)) for 100000 times. Noise level. Since the absorption of the supersonic jet is estimated to be less than 1 mm absorbance, it can be measured for the first time by the present invention. The present invention is not limited to the configuration of the embodiment, but can be appropriately changed within the scope of the claims, for example, by controlling the timing of irradiating the chopper with the light source as a continuous light source.

[0012]

According to the present invention, since the same sample is repeatedly detected and integrated, the sensitivity can be increased. In the case where the detection is performed by performing wavelength scanning, temporal movement of the state is unavoidable. Therefore, the improvement of the S / N ratio is limited even by long-time measurement. However, in the present invention, since multiple wavelengths are simultaneously detected, By increasing the number of repetitions, the S / N ratio is improved and high sensitivity measurement is achieved. As described above, according to the present invention, it is possible to measure the light absorption spectrum of a dilute supersonic jet gas. Since the same optical path as that of the measurement signal is used to obtain the reference signal, and the detection is performed during a period in which the supersonic jet of the sample is not generated, the configuration is simplified.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment.

FIG. 2 is a timing chart showing the operation of the embodiment.

FIG. 3 is a waveform chart showing an integrated average result obtained in one embodiment.

FIG. 4 is a configuration diagram schematically showing a conventional laser supersonic jet spectrometer.

[Explanation of symbols]

 Reference Signs List 20 sample chamber 22 nozzle 23 supersonic jet 28 personal computer 30 interface 32 xenon lamp 36 lamp power supply 40 spectrometer 44 diffraction grating 46 diode array sensor

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-178339 (JP, A) JP-A-4-59456 (JP, U) Totaro Imasaka, "Low-Temperature Spectroscopy", Bunseki, Japan Published by The Society of Analytical Chemistry, 1986, Issue 3, pp. 147-154 (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/74 G01N 1 / 28 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A sample chamber for intermittently ejecting a gas containing a sample as a supersonic jet into a vacuum, a light source for irradiating white light or polychromatic light to the supersonic jet of the sample chamber, and passing through the sample chamber. A light receiving optical system that splits light and detects multiple wavelengths simultaneously, and a detection signal from the light receiving optical system when a jet is generated in the sample chamber is used as a measurement signal, and when a jet is not generated in the sample chamber. A jet spectrometer comprising: a signal processing unit that repeatedly takes in the same sample as a reference signal using the detection signal from the light receiving optical system as a reference signal, performs integration averaging, and calculates absorbance from both detection values.