Laser Induced Fluorescence (LIF) Spectroscopy of Alkoxy Radicals

 

 

The importance of alkoxy radicals (RO·) in atmospheric chemistry is well known. They are key intermediates in the oxidation of hydrocarbons. In our lab, alkoxy radicals are studied by laser-induced fluorescence (LIF) spectroscopy, with both medium and high resolution.

 

The alkoxy radicals are generated in a supersonic free jet expansion by UV laser photolysis of the corresponding alkyl nitrites (RONO). The moderate-resolution (mod-res, FWHM ~0.1cm-1)LIF spectroscopy allows us to record vibrationally resolved spectra of the alkoxy radicals, as well as to measure their fluorescence lifetime, while the high-resolution (hi-res, FWHM ~200-300MHz) LIF spectroscopy is be able to provide us with rotationally resolved spectra.

 

Schematic diagrams of the moderate- and the high-resolution experimental setup are shown in Figure 1 and Figure 2, respectively.

 

So far, LIF spectroscopy of primary alkoxies (containing up to 12 carbon atoms), secondary alkoxies (containing up to 7 carbon atoms), and cyclohexoxy has been studied in our group. A full list of the alkoxy radicals that we have studied is available. As an example, the moderate- and high-resolution LIF spectra of 1-propoxy (C3H7O·) are given in Figure 3 and Figure 4, respectively.

 

Rotational analysis has been done by simulations and eventually fits using the graphical interface program SpecView. Different rotational structures can be assigned to different conformers. Simulations of Band A and Band B of 1-propoxy are shown in Figure 5. They are assigned to G-(gauche-, ) and T(trans-, ) conformers, respectively. Details can be found in Selected Publication 1 and 2.

 

Most recently, we improved the calibration system in our high-resolution LIF setup by introducing Doppler-free absorption spectroscopy of molecular iodine. Accuracy of ~50MHz has been obtained. The experimental setup is shown in Figure 6 and one example of methoxy radical (showing the spin-rotation splitting) is given in Figure 7.

 

When combined with other spectroscopic techniques, LIF spectroscopy can be even more powerful. Figure 8 and Figure 9 show the experimental setup of Dispersed Fluorescence Spectroscopy (DF) and Fluorescence-Depletion Infrared Spectroscopy.

 


 

Selected Publications:

  • "Rotationally Resolved tildeB-tildeX Electronic Spectra of Both Conformers of the 1-Propoxy Radical,'' S. Gopalakrishnan, C. C. Carter, L. Zu, V. Stakhursky, G. Tarczay and T. A. Miller, J. Chem. Phys., 118, 4954 (2003). pub296.pdf

  • "Theoretical Prediction of Spectroscopic Constants of 1-alkoxy Radicals." G. Tarczay, S. Gopalakrishnan, and T. A. Miller, J. Mol. Spectros. , 220, 276, (2003). pub298.pdf
  • "Jet-Cooled LIF Spectra of the Cyclohexoxy Radical," L. Zu, G. Tarczay, J. Liu, T. A. Miller, J. Chem. Phys. 120, 10579 (2004). pub303.pdf supplementary.pdf

  • "The Rotationally Resolved Electronic Spectra of Several Conformers of 1-Hexoxy and 1-Heptoxy," L. Zu, J. Liu, S. Gopalakrishnan, T. A. Miller, Can. J. Chem (Herzberg Memorial Issue 82, 854 (2004). .pub304.pdf

  • " Dispersed Fluorescence Spectroscopy of Primary and Secondary Alkoxy Radicals," J. Jin, I. Sioutis, G. Tarczay, S. Gopalakrishnan, A. Bezant, T. A. Miller, J. Chem. Phys. 121, 11780 (2004). pub305.pdf supplementary.pdf


 

 Full List of  Alkoxy Radicals Studied by LIF/DF in GOES:

 

#Carbon Alkoxy Radicals LIF/DF Spectra Publications
  172. ``The Implications of the Rotationally Resolved Spectra of the Alkoxy Radicals for their Electronic Structure,'' S. C. Foster, Y.-C. Hsu, C. P. Damo, X. Liu, C.-Y. Kung, and T. A. Miller, J. Phys. Chem.90, 6766 (1986).
1 Methoxy Mod-Res LIF

Origin Band (unpublished data)

Hi-Res LIF (unpublished data)

DF

181. ``The Free Jet-Cooled Laser-Induced Fluorescence Spectrum of Methoxy. Part I: Vibronic Analysis of the tildeA and tildeX States,'' S. C. Foster, P. Misra, T.-Y. Lin, C. P. Damo, C. C. Carter, and T. A. Miller, J. Phys. Chem. 92, 5914 (1988).
182. ``The Free Jet-Cooled Laser-Induced Fluorescence Spectrum of Methoxy. Part II: Rotational Analysis of the tildeA2A1tildeX2E Electronic Transition,'' X. Liu, C. P. Damo, T.-Y. Lin, S. C. Foster, P. Misra, L. Yu, and T. A. Miller, J. Phys. Chem. 93, 2266 (1989).
190. ``The Spin-Rotation Interactions in the Methoxy Radical,'' X. Liu, S. C. Foster, J. M. Williamson, L. Yu, and T. A. Miller, Molec. Phys.69, 357 (1990).
255. ``Rovibronic Analysis of Laser Induced Fluorescence Excitation Spectrum of the Jet-Cooled Methoxy Radical,'' D. E. Powers, M. Pushkarsky, and T. A. Miller, J. Chem. Phys. 106, 6868 (1997).
2 Ethoxy Mod-Res LIF 231. ``Rotationally Resolved Electronic Excitation Spectra of the Ethoxy tildeBtildeX Transition,'' X. Q. Tan, J. M. Williamson, S. C. Foster, and T. A. Miller, J. Phys. Chem. 97, 9311 (1993).
  283. ``Jet-cooled Laser Induced Fluorescence Spectroscopy Some Alkoxy Radicals,'' C. Carter, J. R. Atwell, S. Gopalakrishnan, and T. A. Miller, J. Phys. Chem. A 104, 9165 (2000)
3-10 Primary Alkoxy Radicals Mod-Res LIF

Origin Bands

289. ``Laser Excitation Spectra of Large Alkoxy Radicals Containing 5 to 12 Carbon Atoms," S. Gopalakrishnan, C. C. Carter, J. Atwell, and T. A. Miller, J. Phys. Chem., 105, 2925 (2001).
Secondary Alkoxy Radicals Mod-Res LIF

Origin Bands

3 1-Propoxy Mod-Res LIF

Hi-Res LIF

296. ``Rotationally Resolved tildeB-tildeX Electronic Spectra of Both Conformers of the 1-Propoxy Radical,'', S. Gopalakrishnan, C. C. Carter, L. Zu, V. Stakhursky, G. Tarczay and T. A. Miller, J. Chem. Phys., 118, 4954 (2003).
4 1-Butoxy Mod-Res LIF

Hi-Res LIF

297. "Rotationally Resolved Electronic Spectra of the tildeB-tildeX Transition in Multiple Conformers of 1-Butoxy and 1-Pentoxy Radicals." S. Gopalakrishnan, L. Zu, and T. A. Miller, J. Phys. Chem. A , 107, 5189 (2003). Supplementary Material (PDF)
5 1-Pentoxy Mod-Res LIF

Hi-Res LIF

  298. "Theoretical Prediction of Spectroscopic Constants of 1-alkoxy Radicals." G. Tarczay, S. Gopalakrishnan, and T. A. Miller, J. Mol. Spectros. , 220, 276, (2003).
  302. "Natural Lifetimes of Selected Vibronic Levels of tildeB State of Alkoxy," S. Gopalakrishnan, L. Zu, T. A. Miller, Chem. Phys. Lett., 380, 749 (2003).
6 1-Hexoxy Mod-Res LIF(Conformationally Assigned)

Hi-Res LIF (a, b, c)

304. "The Rotationally Resolved Electronic Spectra of Several Conformers of 1-Hexoxy and 1-Heptoxy," L. Zu, J. Liu, S. Gopalakrishnan, T. A. Miller, Can. J. Chem (Herzberg Memorial Issue 82, 854 (2004).
7 1-Heptoxy
3-10 Primary Alkoxy Radicals
3 1-Propoxy DF 305. " Dispersed Fluorescence Spectroscopy of Primary and Secondary Alkoxy Radicals," J. Jin, I. Sioutis, G. Tarczay, S. Gopalakrishnan, A. Bezant, T. A. Miller, J. Chem. Phys. 121, 11780 (2004). supplementary.pdf
4 1-Butoxy DF
3 2-Propoxy DF
4 2-Butoxy DF
6 Cyclohexoxy Mod-Res LIF

Hi-Res LIF

DF

303. "Jet-Cooled LIF Spectra of the Cyclohexoxy Radical," L. Zu, G. Tarczay, J. Liu, T. A. Miller, J. Chem. Phys. 120, 10579 (2004). supplementary.pdf
4 2-Butoxy Mod-Res LIF

Hi-Res LIF

DF

308. "Rotational Analysis of the tildeB-tildeX Electronic Transition of the Conformers of the 2-Butoxy Radical," L. Zu, V. Stakhursky and T. A. Miller.