本實驗使用單色共振雙光子游離光譜術、雙色共振雙光子游離光譜術以及質量解析臨界游離光譜術來探討3,4-二氟苯酚以及2,5-二氟苯酚的分子特性，並且利用上述的光譜術去獲得此分子的第一電子激發態能量、游離能以及經由第一電子激發態和離子態的振動光譜。因為3,4-二氟苯酚以及2,5-二氟苯酚這兩個分子皆具有兩種不同的旋轉異構物，分別為順式3,4-二氟苯酚和反式3,4-二氟苯酚以及順式2,5-二氟苯酚和反式2,5-二氟苯酚。順式3,4-二氟苯酚和反式3,4-二氟苯酚所獲得的躍遷能和游離能分別是35 486 ± 2和35 704 ± 2 cm-1以及70 016 ± 5 和70 203 ± 5 cm-1；而順式2,5-二氟苯酚和反式2,5-二氟苯酚的躍遷能和游離能分別為36 448 ± 2和36 743 ± 2 cm-1以及71 164 ± 5和71 476 ± 5 cm-1。我們可以觀察到在反式結構中，其躍遷能和游離能都略高於順式的結構。經由光譜分析所獲得的結果顯示出造成此結果的原因為平面運動苯環的變形和取代基彼此互相作用有關。綜合三種光譜術所獲得的光譜分析，可得到一個結論，在順式和反式的旋轉異構物中，不管是利用在電子激發的中性物種或是在陽離子基態，其分子的幾何形狀和振動座標都是相似的。

We applied the resonant two-photon ionization and mass-analyzed threshold ionization techniques to record the vibronic and cation spectra of 3,4-difluorophenol (34DFP) and 2,5-difluorophenol (25DFP). The band origins of the S1 ← S0 electronic transition of the cis and trans rotamers of 34DFP are found to be 35 486 ± 2 and 35 704 ± 2 cm-1 and the adiabatic ionization energies are 70 016 ± 5 and 70 203 ± 5 cm-1, respectively. The excitation energy of the S1 ← S0 electronic transition of the cis and trans rotamers of 25DFP are found to be 36 448 ± 2 and 36 743 ± 2 cm-1 and the adiabatic ionization energies are 71 164 ± 5 and 71 476 ± 5 cm-1, respectively. The distinct spectral features mainly result from the in-plane ring deformation and substituent-sensitive bending vibrations. Spectral analysis suggests that the molecular geometry and vibrational coordinates of the cation in the D0 state resemble those of the neutral species in the S1 state for both cis and trans rotamers.

[1] T. Ebata, A. Fujii, N. Mikami, Vibrational spectroscopy of small-sized hydrogen-bonded clusters and their ions, Int. Rev. Phys. Chem. 17 (1998) 331-361.
[2] T. Watanabe, T. Ebata, N. Mikami, Size‐selected vibrational spectra of phenol‐(H2O) n (n=1–4) clusters observed by IR–UV double resonance and stimulated Raman‐UV double resonance spectroscopies, J. Chem. Phys. 105 (1996) 408-419.
[3] G. Brehma, G. Sauera, N. Fritza, S. Schneidera, S. Zaitsev, Correlation spectroscopy based on non-linear response of silver colloids (including SEHRS), J. Mol. Struct. 735 (2005) 85-102.
[4] D.E. Powers, J.B. Hopkins, R.E. Smalley, Vibrational relaxation in jet‐cooled phenylalkynes, J. Chem. Phys. 74 (1981) 5971-5976.
[5] J.M. Dyke, H. Ozeki, M. Takahashi, M.C.R. Cockett, K. Kimura, A study of phenylacetylene and styrene, and their argon complexes PA–Ar and ST–Ar with laser threshold photoelectron spectroscopy, J. Chem. Phys. 97 (1992) 8926-8933.
[6] T. Isozaki, K. Sakeda, T. Suzuki, T. Ichimura, Fluorescence spectroscopy of jet-cooled o-fluoroanisole: Mixing through Duschinsky effect and Fermi resonance, J. Chem. Phys. 132 (2010) 214308 (9 pages).
[7] J.S. Lee, S.A. Krasnokutski, D.S. Yang, High-resolution electron spectroscopy and structures of lithium-nucleobase (adenine, uracil, and thymine) complexes, J. Chem. Phys. 132 (2010) 044304 (8 pages).
[8] K. Watanabe, Electron-microscopical studies on the inner structure of paramecium-caudatum by means of ultra-thin sections, J. Chem. Phys. 22 (1954) 1564-1570.
[9] D.W. Turner, M.I. AlJoboury, Determination of ionization potentials by photoelectron energy measurement, J. Chem. Phys. 37 (1962) 3007-3008.
[10] L.A. Chewter, M. Sander, K. Muller-Dethlefs, E.W. Shlag, High resolution zero kinetic energy photoelectron spectroscopy of benzene and determination of the ionization potential, J. Chem. Phys. 86 (1987) 4737-4744.
[11] G.C. King, A.J.Yencha, M.C.A. Lopes, Threshold photoelectron spectroscopy using synchrotron radiation, J. Electron Spectrosc. Relat. Phenom. 114 (2001) 33-40.
[12] T. Bear, Y. Li, Threshold photoelectron spectroscopy with velocity focusing: an ideal match for coincidence studies, Int. J. Mass Spectrom. 219 (2002) 381-389.
[13] K. Muller-Dethlefs, M. Sander, E.W. Schlag, 2-color photoionization resonance spectroscopy of no - complete separation of rotational levels of no+ at the ionization threshold, Chem. Phys. Lett. 112 (1984) 291-294.
[14] L. Zhu, P.M. Johnson, Mass analyzed threshold ionization spectroscopy, J. Chem. Phys. 94 (1991) 5769-5771.
[15] H. Krause, H.J. Neusser, Dissociation of state-selected complex-ions studied by mass-selective pulsed field threshold ionization spectroscopy, J. Chem. Phys. 97 (1992) 5923-5926.
[16] L. Zhu, P.M. Johnson, Vibrations of pyrazine and its ion as studied by threshold ionization spectroscopy, J. Chem. Phys. 99 (1993) 2322-2331.
[17] X. Zhang, J.M. Smith, Dynamics of high n molecular Rydberg states with application to mass analyzed threshold ionization spectroscopy, J.L. Knee, J. Chem. Phys. 99 (1993) 3133-3136.
[18] C.W. Hsu, K.T. Lu, M. Evans, Y.J. Chen, C.Y. Ng, P. Heimann, A high resolution photoionization study of Ne and Ar: Observation of mass analyzed threshold ions using synchrotron radiation and direct current electric fields, J. Chem. Phys. 105 (1996) 3950-3961.
[19] K.W. Lo, W.B. Tzeng, 3-Chloro-4-fluoroaniline studied by resonant two-photo ionization and mass-analyzed threshold ionization spectroscopy, J. Mol. Spectrosc. 288 (2013) 1-6.
[20] W.C. Huang, P.S. Huang, C.H. Hu, W.B. Tzeng, Resonant two-photon mass-analyzed threshold ionization of 2,5-difluoroaniline, Chem. Phys. Lett. 580 (2013) 28-31.
[21] H.C. Huang, K.S. Shiung, B.Y. Jin, W.B. Tzeng, Rotamers of m-chloroanisole studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy, Chem. Phys. 425 (2013) 114-120.
[22] V. Shivatare, W. B. Tzeng, Spectroscopic Investigation of cis-2,4-difluorophenol cation by mass-analyzed threshold ionization spectroscopy, Bull. Korean Chem. Soc. 35 (2014) 815-820.
[23] V. Shivatare, Q. Zheng, B. Zhang, T. Ganguly, W.B. Tzeng, Mass-analyzed threshold ionization spectroscopy of trans-1-methoxynaphthalene cation and the methoxyl substitution effect, J. Mol. Spectrosc. 284-285 (2013) 16-20.
[24] O. Dopfer, K. Müller-Dethlefs, S1 excitation and zero kinetic energy spectra of partly deuterated 1:1 phenol–water complexes, J. Chem. Phys. 101 (1994) 8508-8516.
[25] S.R. Haines, W.D. Geppert, D.M. Chapman, M.J. Watkins, C.E.H. Dessent, M.C.R. Cockett, K. Müller-Dethlefs, Evidence for a strong intermolecular bond in the phenol center dot N-2 cation, J. Chem. Phys. 109 (1998) 9244-9251.
[26] L.W. Yuan, C.Y. Li, J.L. Lin, S.C. Yang, W.B. Tzeng, Mass analyzed threshold ionization spectroscopy of o-fluorophenol and o-methoxyphenol cations and influence of the nature and relative location of substituents, Chem. Phys. 323(2006) 429-438.
[27] K. Yosida, K. Suzuki, S. Ishiuchi, M. Sakai, M. Fujii, C.E.H. Dessent, K. Müller-Dethlefs, The PFI-ZEKE photoelectron spectrum of m-fluorophenol and its aqueous complexes: Comparing intermolecular vibrations in rotational isomers, Phys. Chem. Chem. Phys. 4 (2002) 2534-2538.
[28] B. Zhang, C. Li, H. Su, J.L. Lin, W.B. Tzeng, Chem. Mass analyzed threshold ionization spectroscopy of p-fluorophenol and the p-fluoro substitution effect, Chem. Phys. Lett. 390 (2004) 65-70.
[29] Y. Xu, S.Y. Tzeng, B. Zhang, W.B. Tzeng, Rotamers of 3,4-difluoroanisole studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy, Spectrochim. Acta A 102 (2013) 365-370.
[30] J.L. Lin, W.B. Tzeng, Two-color resonant two-photon mass analyzed threshold ionization spectroscopy of aromatic molecules, Trends in Appl. Spectrosc. 5 (2004) 71-82.
[31] W.C. Huang, W.B. Tzeng, Rotamers of aromatic molecules studied by two-color resonant two photon ionization and mass-analyzed threshold ionization spectroscopy, Trends in Appl. Spectrosc. 9 (2013) 75-84.
[32] P.M. Johnson, E.C. Otis, Molecular multiphoton spectroscopy with ionization detection , Annu. Rev. Phys. Chem. 32 (1981) 139-257.
[33] U. Boesl, H.J. Neusser, E.W.Schlag, Multi-photon ionization in the mass spectrometry of polyatomic molecules: Cross sections, Chem. Phys. 55 (1981) 193-204.
[34] H. Su, M. Pradhan, W.B. Tzeng, Mass analyzed threshold ionization spectroscopy of indazole cation, Chem. Phys. Lett. 411 (2005) 86-90.
[35] J.L. Lin, Y.C. Li, W.B. Tzeng, Mass analyzed threshold ionization spectroscopy of aza-aromatic bicyclic molecules: Benzimidazole and benzotriazole , Chem. Phys. 334 (2007)189-195.
[36] M.A. Smith, J.W. Hager, S.C. Wallace, Two color photoionization spectroscopy of jet cooled aniline: Vibrational frequencies of the aniline X̃2 B 1 radical cation, J.Chem.Phys. 80 (1984) 3097-3105.
[37] M.A. Duncan, T.G. Deltz, R.E. Smalley, Two‐color photoionization of naphthalene and benzene at threshold , J.Chem.Phys. 75 (1981) 2118-2125.
[38] K. Kimura, Development of laser photoelectron spectroscopy based on resonantly enhanced multiphoton ionization, J.E. Spectrosc. Relat. Phenom. 100 (1999) 273-296.
[39] H. Ikoma, K. Takazawa, Y. Emura, S. Ikeda, H. Abe, H. Hayashi, M. Fujii, Internal rotation of methyl group in o‐ and m‐toluidine cations as studied by pulsed field ionization–zero kinetic energy spectroscopy, J. Chem. Phys. 105 (1996) 10201-10209.
[40] F. Merk, Molecules in high rydberg states, Annu. Rev. Phys. Chem. 48 (1997) 675-709.
[41] A. Held, E.W. Schlag, Kluwer Academic Publishers. (1991) 249.
[42] W.A. Chupka, Factors affecting lifetimes and resolution of Rydberg states observed in zero‐electron‐kinetic‐energy spectroscopy, J. Chem. Phys. 98 (1993) 4520-4530.
[43] J.L. Lin, W.B. Tzeng, Mass analyzed threshold ionization of deuterium substituted isotopomers of aniline and p-fluoroaniline: Isotope effect and site-specific electronic transition, J.Chem.Phys.115 (2001) 743-751.
[44] J.L. Lin, J.L. Lin, W. B. Tzeng, Mass analyzed threshold ionization spectroscopy of N-deuterium substituted indoline cation: Isotope effect on the electronic transition, ionization and molecula vibration, Chem. Phys. Lett. 371 (2003) 662-669.
[45] J.L. Lin, J.L. Lin, W.B. Tzeng, Mass analyzed threshold ionization spectroscopy of N-methylaniline and N-ethylaniline cations: Isotope effect on transition energy and large amplitude vibrations, J. Chem. Phys. 295 (2003) 97-107.
[46] L.W. Yuan, C.Li, W.B. Tzeng, Site-specific H/D exchange of p-methoxyphenol studied by resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy, J. Chem. Phys. A.109 (2005) 9481-9487.
[47] S. Georgiev, H. J. Neusser, Investigation of hydrogen bonding in 3-methylindole • H2O cluster by mass analyzed threshold ionization, Chem. Phys. Lett. 389 (2004) 24-28.
[48] J.L. Lin, C.J. Huang, C.H. Lin, W. B. Tzeng, Resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of the selected rotamers of m-methoxyaniline and o-methoxyaniline, J. Mol. Spectrosc. 244 (2007) 1-8.
[49] J.L. Lin, L.C.L. Huang, W.B. Tzeng, Mass-analyzed threshold ionization spectroscopy of the selected rotamers of hydroquinone and p-dimethoxybenzene cations, J. Phys. Chem. A.105 (2001) 11455-11461.
[50] John H. Moore, Christopher C. Davis, Michael A. Coplan, Sandra C. Greer, Building scientific apparatus, University of Maryland,College Park, 2002
[51] User’s manual (Spectra-Physics LAB-150)
[52] Exciton Laser Dyes 30 Years of Excellence and More Brilliant Than Ever.
[53] O. Dopfer, G. Reiser, K. Muller-Dethlefs, E.W. Schlag, S.D. Colson, Zero‐kinetic‐energy photoelectron spectroscopy of the hydrogen‐bonded phenol‐water complex, J. Chem. Phys. 101 (1994) 974-989.
[54] M.J. Frisch et al., Gaussian 09, Revision A.02, Gaussian, Inc., Wallingford, CT, 2009.
[55] J.B. Foresman, A. Frsch, Exploring Chemistry with Electronic Structure Methods, Gaussian, Inc., 1996.
[56] J.A. Pople, R.K. Nesbet, Self-consistent orbitals for radicals, J. Chem. Phys. 22 (1954) 571-572.
[57] R. McWeeny, G. Dierksen, Studies in configuration interaction. ii. determination of charge‐ and spin‐density functions in π‐electron systems, J. Chem. Phys. 49 (1968) 4852-4856.
[58] P. Hohenberg, W. Kohn, Inhomogeneous electron gas, Phys. Rev. 136 (1964) B864-B871.
[59] W. Kohn, L.J. Sham, Self-consistent equations including exchange and correlation effects, Phys. Rev. 140 (1965) A1133-A1138.
[60] A.D. Becke, Density‐functional thermochemistry. II. The effect of the Perdew–Wang generalized‐gradient correlation correction, J. Chem. Phys. 97 (1992) 9173-9177.
[61] P.M.W. Gill, B.G. Johnson, J.A. Pople, M.J. Frisch, The performance of the Becke-Lee-Yang-Parr (B-LYP) density functional theory with various basis-sets, Chem. Phys. Lett. 197 (1992) 499-505.
[62] G.A. Petersson, A. Bennett, T.G. Tensfeldt, M.A. Al-Laham, W.A. Shirley, J. Mantzaris, A complete basis set model chemistry. I. The total energies of closed‐shell atoms and hydrides of the first‐row elements, J. Chem. Phys. 89 (1988) 2193-2218.
[63] G.A. Petersson, M.A. Al-Laham, A complete basis set model chemistry. II. Open‐shell systems and the total energies of the first‐row atoms, J. Chem. Phys. 94 (1991) 6081-6090.
[64] J.B. Foresman, M. Head-Gordon, J.A. Pople, M.J. Frisch, Toward a systematic molecular-orbital theory for excited-states, J. Phys. Chem. 96 (1992) 135-149.
[65] M.E. Casida, C. Jamorski, K.C. Casida, D.R. Salahub, Molecular excitation energies to high-lying bound states from time-dependent density-functional response theory: Characterization and correction of the time-dependent local density approximation ionization threshold, J. Chem. Phys. 108 (1998) 4439-4449.
[66] W.J. Hehre, R.F. Stewart, J.A. Pople, Self‐consistent molecular‐orbital methods. i. use of gaussian expansions of slater‐type atomic orbitals, J. Chem. Phys. 51 (1969) 2657-2664.
[67] M.J. Frisch, J.A. Pople, J.S. Binkley, Self‐consistent molecular orbital methods 25. Supplementary functions for Gaussian basis sets, J. Chem. Phys. 80 (1984) 3265-3269.
[68] G. Varsanyi, Assignments for Vibrational Spectra of Seven Hundred Benzene Derivatives,Wiley, New York, 1974
[69] T. Vondrak, S.I. Sato, K. Kimura, Cation vibrational spectra of indole and indole-argon van der Waals complex. A zero kinetic energy photoelectron study, J. Phys. Chem. A. 101 (1997) 2384-2389.
[70] E. Bright Wilson, Physical Review. Volum 45 (1934)
[71] A. Oikawa, H. Abe, N. Mikami, M. Ito, Electronic spectra and ionization potentials of rotational isomers of several disubstitued benzenes. [cis-m-fluorophenol, S100= 36623 cm-1, IE = 70164 cm-1; trans-m-fluorophenol, S100= 36830 cm-1, IE = 70425 cm-1], Chem. Phys. Lett. 116 (1985) 50-54.
[72] C.Y. Tsai, W.B. Tzeng, Rotamers of 3,4-difluorophenol studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy, Journal of Photochemistry and Photobiology A: Chemistry 270 (2013) 53-58.
[73] M. Shinozaki, M. Sakai, S. Yamaguchi, T. Fujioka, M. Fujii, S1–S0 Electronic spectrum of jet-cooled m-aminophenol, Phys. Chem. Chem. Phys. 5 (2003) 5044-5050.
[74] Y. Xie, H. Su, W.B. Tzeng, Rotamers of m-aminophenol cation studied by mass analyzed threshold ionization spectroscopy and theoretical calculations, Chem. Phys. Lett. 394 (2004) 182-186.
[75] J.R. Lombardi, Dipole moments of the lowest singlet π* ← π states in phenol and aniline by the optical stark effect, J. Chem. Phys. 50 (1969) 3780-3783.
[76] K.T. Huang, J.R. Lombardi, Dipole moments of the lowest singlet π* ← π states in p-fluorophenol and p-fluoroaniline, J. Chem. Phys. 51 (1969) 1228-1230.
[77] A. Gaber, M. Riese, J. Grotemeyer, Mass analyzed, threshold ionization spectroscopy of o-, m-, and p-dichlorobenzenes. Influence of the chlorine position on vibrational spectra and ionization energy, J. Phys. Chem. A 112 (2008) 425-434.
[78] S.C. Yang, J.L. Lin, W.B. Tzeng, Mass analyzed threshold ionization spectroscopy of p-ethylaniline cation: Alkyl chain effects on ionization and molecular vibration, Chem. Phys. Lett. 362 (2002) 19-25.
[79] K.S. Shiung, D. Yu, W.B. Tzeng, Rotamers of m-fluoroanisole studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy, J. Mol. Spectrosc. 274 (2012) 43-47.
[80] K.S. Shiung, D. Yu, S.Y. Tzeng, W.B. Tzeng, Cation spectroscopy of o-fluoroanisole and p-fluoroanisole by two-color resonant two-photon mass-analyzed threshold ionization, Chem. Phys. Lett. 524 (2012) 38-41.