Research

我們感興趣的是在大氣、燃燒、或行星化學，但難以用傳統技術來檢測的不穩定物種或自由基。藉由做各種實驗來研究它們的光譜學、動力學和動態學，並使用理論計算來幫助理解問題。
代表性技術包括：

1. 步進式掃描霍氏紅外光譜：在吸收模式​​中，檢測反應中間體，如：Criegee中間體CH₂OO和它們的反應中間體之光譜。在放光模式中，觀測光解或雙分子反應所形成產物的轉動和振動狀態，瞭解它們的動態學。此技術領先世界。
2. 質量選擇的紅外光譜：使用真空紫外光游離-飛行時間質譜法檢測分子。如果在分子被游離前照射紅外雷射光，通過觀察各個離子的信號隨紅外光波長的變化，可以推導出團簇體或自由基的質量選擇的紅外光譜。
3. 仲氫間質隔離：仲氫是量子固體，已經成為一種新型的間質主體，可在3 K溫度下隔離不穩定的物種。利用其極小的晶格效應的優勢，我們可產生各種自由基並用紅外光或螢光檢測之。還可用電子撞擊來產生質子化的物種。
4. 超快光譜：探討固態材料和溶液在飛秒範圍的動態學。主要儀器設備：飛秒雷射系統、準分子雷射、Nd：YAG雷射、染料雷射、 紅外雷射、步進掃描式霍氏紅外光譜儀、低溫系統（3 K或10 K） 、飛行時間質譜、共振腔衰盪系統、 螢光光譜儀。

MATRIX

     The matrix-isolation technique has served to produce and to trap novel chemical species in diverse chemical and physical problems since its inception in 1954.1 Several books on matrix-isolation techniques and their applications have covered various aspects of this simple yet useful technique. In addition to its capability of trapping and preserving unstable species, the matrix-isolation technique has an additional advantage in accumulating the sample via continuous deposition for a protracted period to facilitate detection of weak absorption lines due to a small cross section or small concentration. Furthermore, the sample required in the experiment is small relative to that in gas-phase experiments; use of precious samples such as isotopic variants and specially synthesized precursors thus becomes feasible.

     The photochemical behavior of species isolated in matrices might be distinct from that in the gaseous phase. In the gaseous phase at small pressure, fragments have little chance to collide with each other upon photodissociation, whereas photofragments produced in a matrix are typically constrained within the matrix cage; consequently they might collide with each other several times at various impact angles and eventually react with each other. For these types of “cage” reactions, the chance for photofragments to collide with each other within a certain acceptance cone is much greater than in the gaseous phase; hence the possibility of producing various isomers of the original precursor or other stable products or their complex is much increased. The low temperature and the efficient relaxation of energy by the matrix host further enhance the formation of unstable intermediates that are produced with difficulty in the gaseous phase.

• p-H₂ Matrix
• Unstable Molecule

For more information, please see:  Phys. Chem. Chem. Phys. 16, 2200 (2014).
Last Updated ( Mar. 4, 2016 )

STEP-SCAN FTIR (ABSORPTION)

     An infrared spectrum provides molecular information about the vibrational modes, the types of transitions, and the transition probability. Using Fourier-transform infrared spectrometer, we can readily obtain simultaneously those pieces of information about stable molecules. The main concept of absorption is population difference: if the population difference is large, strong absorption might occur, but a small population difference causes a weak absorption. When molecules are populated mainly in the ground state, the absorption method functions whereas the emission approach fails. Hence, absorption detection serves as an effective method to purvey information about the lower states. Moreover, FTIR equipped with a step-scan mode can elicit excellently both spectral and temporal information in monitoring a rapid chemical phenomenon. The spectral resolution can attain 0.13 cm-1 and temporal resolution up to 50 ns. Much research has been done in the condensed phase through step-scan IR absorption. We extended the method to a gaseous-phase system to investigate both the products upon photolysis and the reaction intermediates.
For more information, please see:  J. Chin. Chem. Soc. 61, 47 (2014)​.
Last Updated ( Mar. 4, 2016 )

CAVITY RINGDOWN

     By comparison with conventional absorption spectroscopy that involves the measurement of a small change in a large signal due to radiation transmitted through an absorbing material, causing a condition of a large background that results in a small sensitivity, cavity ringdown spectroscopy (CRD) is a sensitive method that relies on the measurement of the rate of decay of radiation trapped in a short cavity (e.g. our cavity length is 90 cm) formed between two highly reflective mirrors (~99.99 %), producing a long optical path (length ~9 km for a 90-cm cavity) that bestows great sensitivity. With CRD, one is thereby able to measure an extremely weak absorption with a large quantity or a minute quantity with strong absorption to achieve a detection limit otherwise unattainable with conventional absorption spectroscopy.
Last Updated ( Feb. 13, 2008 )

IR-VUV TOF

     IR spectra of gaseous free radicals investigated in our laboratory using cavity ring down or time-resolved FTIR absorption are often severely overlapped with those of their precursors. Also, IR spectra of clusters of various sizes are similar. Without size selection or using double resonance, the overlapped spectral region is difficult to study. However, double resonance requires a chromophor that has an electronic state in the UV or visible region for resonant multi-photon ionization. It is thus strongly desirable to develop an IR technique that has mass selectivity so that the interference from other species may be eliminated. Thus, we set up a new system which can overcome this difficulty and has the following features.

1. Having mass selectivity
2. Having energy selectivity with selective ionization
3. With high sensitivity

     In IR-VUV ionization, we employed VUV (118 nm or tunable) emission as a soft ionization light source; the photon energy was chosen to be near ionization threshold, so that molecules don’t further dissociate after ionization. Detection of ions with a time-of-flight system offers high sensitivity and mass selectivity.
Two excitation schemes for IR-VUV ionization are possible for investigation of neutral species.
Last Updated ( June 4, 2010 )

FEMTOSECOND TRANSIENT ABSORPTION SPECTROSCOPY

Updating.

SHOCK TUBE TECHNIQUE (COLLABORATION WITH N. S. WANG)

     The shock tube is the best tool for kinetic experiments in the gaseous phase at high temperatures because it can generate a uniform high-temperature environment. Its operation utilizes a pressure difference to produce the shock wave; then the shock wave compresses the gas in the reactor. We utilize this technique to study the kinetics of reactions; current projects involve reactions of oxygen atoms with other molecules. Oxygen atoms are generated by pyrolysis of N2O or photolysis of SO2; their concentration is detected by vacuum-ultraviolet(VUV) atomic-resonance absorption spectroscopy (ARAS) conventional system produces a shock wave an puncturing of a diaphragm that separates the regions of large and small pressures . Because our experimental system utilizes a diaphragmless piston driver, it is unnecessary to open the reactor so that it becomes contaminated an exposure to ambient air; it can produce a temperature about 2000 K; this characteristic is important in high-temperature research. The shock wave is almost the only choice for research.
Last Updated ( Feb. 13, 2008)