Scientific Research Division

Education

1996－2000  B.S. in Chemistry, National Chung Hsing University (Taiwan)               

2000－2005  Ph.D. in Physical Chemistry, National Tsing Hua University (Taiwan)          

                          

Employment

2002.08－12  Visiting Student, Department of Chemistry, Emory University (USA)

2005.08－10  Postdoc, Dep. Applied Chemistry, National Chiao Tung University (Taiwan)  

2006－2009   Postdoc, Scientific Research Division, National Synchrotron Radiation Research Center (Taiwan)         

2010－2014   Assistant Research Scientist, National Synchrotron Radiation Research Center (Taiwan)

2015－now   Associate Research Scientist, National Synchrotron Radiation Research Center (Taiwan)

 

Award

國家同步輻射研究中心傑出論文獎 (2009－2014)

 

Research Interest

(1) Direct Optical Detection of Molecular Ions:

    In the past half-century, astronomers identified more than 190 kinds of molecules exist in the interstellar mediums via observations of large microwave/terahertz telescopes. Among them, only about 32 species have been found in the ionic forms.  One can image that the number of interstellar ionic species should be more than that observed currently, because high-energy photons and particles filled the interstellar medium that can effectively ionize neutral molecules to form charged molecules. Previously, information regarding structures and energy levels of ionic molecules were mostly obtained by photoelectron spectroscopy (PES) techniques in laboratories. However, astronomical observations are phenomena of either absorptions or emissions from interstellar molecules, PES data cannot directly apply to compare with the astronomical observations. 

 Jacox et al. have successfully measured the IR spectra of many small molecular ions using matrix-isolation spectroscopy coupled with a microwave discharge method; the clear identification of the IR features of molecular ions remains difficult, because ionization of larger molecules via microwave discharge methods may generate complex fragmentations. Here we attempt to produce ions in the matrices and record their IR and UV spectra. The ions are produced by electron bombardment of a matrix sample during matrix deposition. Bands of ionic species changed in intensities when the matrix sample maintained in darkness for a prolonged time because trapped electrons diffuse slowly to neutralize cations in the matrices. Further irradiations of matrix samples with UV light from a synchrotron radiation were performed to understand the photodissociation behaviors of ions.

 

(2) Spectra of Protonated Polycyclic Aromatic Hydrocarbons

    One of the long-standing mysteries in astrochemistry is the source of the so-called unidentified infrared (UIR) emission bands which are observed consistently and universally in the interstellar medium. The interstellar infrared emission is believed to arise from ultraviolet excitation or energetic particles impact of PAHs. The possible carriers of UIR have been expanded to derivatives of PAHs, including cationic PAHs, hydrogenated, and dehydrogenated PAHs, and heteroatom-substituted PAHs. Now It is widely accepted that the carriers of UIR emission are derivatives of PAH in a cationic form. Identification of IR spectra of derivatives of polycyclic aromatic hydrocarbons is important in understanding the UIR emission bands of interstellar media. We develop a new method to study IR spectra of protonated aromatic hydrocarbons with high resolution, true intensity and wide spectral coverage. Moreover, the major products produced in our method are only protonated PAH and its neutral counter part, so that the information regarding structures and fine spectral features of both cationic and neutral species can be obtained clearly and simultaneously. 

    We have developed a new method for investigating the IR spectra of protonated aromatic hydrocarbons and their neutral counterparts using electron bombardment of para-hydrogen (p-H2) during matrix deposition. We used the IR spectra of protonated benzene (C6H7+) and cyclohexadienyl radical (c-C6H7) to demonstrate the advantages of this method. Our results clearly indicate that c-C6H7 and C6H7+ are the only major products and their IR spectra with much improved resolution, signal-to-noise ratio, and spectral coverage were recorded; furthermore, as compared with IR dissociation of Ar-tagged species and IRMPD methods, the IR spectra reflect true IR intensity.

 

(3) Irradiation of Interstellar, Cometary, and Planetary Ices with UV Photons and Energetic Electrons

    In recent years, various frozen molecules on dust grains in the interstellar medium (ISM) have been detected and identified through ground- and space-based infrared observations. These dust grains are thought to play important roles in the interstellar chemistry of cold and dense molecular clouds; in particular, low-temperature chemical reactions can possibly take place in the presence of cosmic ray irradiation. Interstellar grains or icy mantles of cosmic objects are continuously exposed to energetic particles as well as photons that will lead to excitation, dissociation and ionization of molecules. As a consequence, a variety of new species can be produced by reactions among the fragments. 

    Nitriles and nitrile chemistry have attracted more attention compared to other compounds in astrochemistry because they are easily detected both in the gas and solid phases in the ISM, comets, planets, and satellites. In addition, nitrile derivatives are thought to be precursors in the synthesis of amino acids in astrophysical environments, although amino acids have not yet been conclusively detected beyond the Earth. One would expect a method to synthesis molecules containing –CN groups in astrophysical environments to start from the simplest molecules containing N and C atoms, i.e. N2 and CH4, especially as these molecules are common both in the ISM and in our solar system. when exposed to VUV irradiation. These nitriles might play an important role in the synthesis of prebiotic molecules. More importantly, we have measured the column densities of HNC and HCN formation and have investigated their ratios as a function of irradiation time for the first time. The presence of HNC and the variations of HNC/HCN ratios obtained in the present work may improve our understanding of the evolution of icy chemistry on icy bodies in cosmic environments.

 

Selected Publication

1. Irradiation of Ethylene Diluted in Solid Nitrogen with Vacuum Ultraviolet Light and Electrons: Its Implications for the Formation of HCN and HNC. H-F Chen, M-C Liu, S-C Chen, T-P Huang, and Y-J Wu,* Astrophys. J. 804, 36 (2015). 

 

2. Infrared Spectra of Acetylene Diluted in Solid Nitrogen upon Irradiation with Vacuum Ultraviolet light and electrons. Y-J Wu,* S-J Chuang, S-C Chen, and T-P Huang, Astrophys. J. Suppl. Ser. 212, 7 (2014).

 

3. Infrared Spectra of Protonated Coronene and Its Neutral Counterpart in Solid Parahydrogen: Implications for the Unidentified Interstellar Infrared Emission Bands. M. Bahou, Y-J Wu,* and Y-P Lee,* Angew. Chem. Int. Ed. 53, 1021 (2014).

 

4. Far Ultraviolet Absorption Spectra of N3 and N2+ Generated by Electron Impacting Gaseous N2. Y-J Wu,* H-F Chen, S-J Chuang, and T-P Huang, Astrophys. J. 779, 40 (2013).

 

5. Ultraviolet and Infrared Spectra of Electron Bombarded Solid Nitrogen and Methane Diluted in Solid Nitrogen. Y-J Wu,* H-F Chen, S-J Chuang, and T-P Huang, Astrophys. J. 768, 83 (2013).

 

6. Direct spectral evidence of single-axis rotation and ortho-hydrogen-assisted nuclear spin conversion of CH3F in solid parahydrogen. Y-P Lee,* Y-J Wu, and J. T. Hougen, J. Chem. Phys. 129, 104502 (2008) and selected as Editors’ choice in Science 322, 16 (2008).

 

7. Internal rotation and nuclear spin conversion of CH3OH in solid parahydrogen. Y-P Lee,* Y-J Wu, R. M. Lees, L-H Xu and J. T. Hougen, Science, 311, 365 (2006).