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Far ultraviolet resonance raman spectroscopy: New capability and applications in the vacuum ultraviolet region
Journal of Luminescence 40&41 (1988) 827—828 North-Holland, Amsterdam
FAR ULTRAVIOLET RESONANCE RAMAN SPECTROSCOPY: ULTRAVIOLET REGION
827
NEW CAPABILITY AND APPLICATIONS IN THE VACUUM
Bruce HUDSON Department of Chemistry & Chemical Physics Institute, University of Oregon Eugene, Oregon 97403, United States of America* The development and performance of laser techniques for obtaining resonance Raman spectra in the far ultraviolet region will be described. Examples of spectra with radiation as short as 141.2 nm are presented. The utility of this technique as a method for providing valuable new information about excited electronic states and high energy vibrational transitions is illustrated with several examples. The prospects for extension of this technique to even shorter wavelengths and the generation of tunable radiation in this region will be discussed with emphasis on the use of s-barium borate for harmonic generation. Resonance Raman scattering (or resonance
sities of particular ground electronic state
secondary radiation) has long been recognized as a useful method for obtaining information
vibrational bands. The symmetry and the nature of the atomic motions of these vibra-
concerning excited electronic state potential surfaces. Recent advances in laser technology
tions is usually known with some degree of certainty.
now permit the application of this simple technique using ultraviolet radiation. This allows the examination of highly excited
This technique can also be used to establish the electronic symmetry of an excited state if it results in a transition from the ground
electronic states and excitations of small molecules of theoretical interest. These
state that is forbidden by symmetry for the ground state equilibrium geometry. In
high energy electronic excitations, particularly in small molecules, often result in large changes in the molecular geometry
this case the intensity of the transition must come from the transient displacement of the molecule along non-totally symmetric
along certain coordinates. Sometimes photodissociation or isomerization occurs in the excited
modes of vibration. In the linear vibronic coupling approximation this results in the
state. These features of the excitation, in addition to spectral complexity, may
appearance of characteristic two-quantum transitions of this mode. The symmetry of
make the absorption spectrum diffuse and difficult to interpret, The vibrational Raman spectrum observed under conditions of resonance with such excited states often shows clearly the nature
these modes often determines the symmetry of the excited electronic state. This method has been applied to benzene and its deny46 and butadiene7. atives Another interesting aspect of ultraviolet
of the geometry change in the excited state.~3 This information is relatively easy to interpret
resonance Raman spectroscopy is that highly excited vibrational levels of the ground
because it is obtained in the form of inten-
state are often observed that are not found in normal (off-resonance) Raman spectra
*Research supported by grants from the US National Science Foundation (CHE85-11799) US National Institutes of Health (GM32324) 0022—2313/88/$03.50 ©
Elsevier Science Publishers By.
(North-Holland Physics Publishing Division)
828
B. Hudson
/
Far ultraviolet resonance Roman speciroscopy
813 This occurs when or infra-red spectra. the electronic excitation results in a large
4. L.D. Ziegler and B. Hudson, 3. Chem. Phys. 74 (1981) 232.
geometry change. Because of this effect, new information concerning the ground state poten-
5. D.P. Gerrity, L.D. Ziegler, P.B. Kelly, R. A. Desidenio and B. Hudson, 3. Chem. Phys. 83 (1985) 3209.
tial surface is obtained. This new technique has also been applied to molecules of biological interest.1419
6. L.D. Ziegler and B. Hudson, 3. Chem. Phys. 79 (1983) 1134.
The methodology used to obtain ultraviolet
7. R.R. Chadwick, D.P. Gerrity and B. Hudson, Chem. Phys. Lett. 115 (1985) 24.
radiation for these studies2’20 is based on the generation of harmonics of a high power
8. R.A. Desiderio, D.P. Gerrity and B. Hudson Chem. Phys [ett.115 (1985) 29.
Nd:YAG laser at 532, 355, 266 and 213 nm. The radiation at 532, 355 and 266 nm is suffi-
9. L.D. Ziegler and B. Hudson, 3. Phys. Chem. 88 (1984) 1110.
ciently intense that it can be shifted to shorter wavelengths via stimulated Raman scattening. If hydrogen gas is used as the Raman shifting medium, the new radiation differs
10. L.D. Ziegler, P.B. Kelly and B. Hudson, 3. Chem. Phys. 81 (1984) 6399. 11. P.B. Kelly and B. Hudson, Chem. Phys. Lett. 114 (1985) 451.
from the input by multiples of the vibrational -l frequency of hydrogen, 4155 cm . Thus, for
12. L.D. Ziegler and B. Hudson, 3. Chem. Phys. 79 (1983) 1197.
example, input radiation at 266 nm results in output radiation at 240, 218, 200, 184, 171, 160, 150, 141, 133 nm etc. The shortest
13. R.J. Sension, [.C.Mayne and B. Hudson, 3. Am. Chem. Soc. 109 (1987) 5036.
wavelength used for Raman scattering to date is 141.2 nm.13 The recently developed non-linear optical crystal s-barium borate 21 permits generation of 213 nm radiation with sufficient intensity that stimulated Raman shifting should be possible and even shorter wavelengths can
.
14. B. Hudson and L.C. Mayne in: Biological Applications of Raman Spectroscopy, ed. T.G. Spiro (John Wiley, New York, 1987) pp. 181200. 15. B. Hudson and L.C. Mayne, Meth. 130 (1986) 331.
Enzymol.,
16. [.0.Ziegler, B. Hudson, D.P. Strommen and W.L. Peticolas, Biopolymers 23 (1984) 2067.
be generated. 17. W.L. Kubasek, B. Hudson and W. L. Peticolas, Proc. Nat. Acad. Sci. USA 82 (1985) 451. REFERENCES
18. L.C. Wayne, L.D. Ziegler and B. Hudson, 3. Phys. Chem. 89 (1985) 3395.
1. B. Hudson, Spectroscopy, 1 (1986) 22. 2. B. Hudson, P.8. Kelly, L.D. Ziegler, R.A. Desiderio, D.P. Gerrity, W. Hess and R. Bates in: Advances in Laser Spectroscopy, Volume 3, eds. B.A. Garetz and 3.R. [ombardi, (John Wiley & Sons, New York, 1986) pp. 1-32. 3. B. Hudson in: Time-Resolved Vibrational Spectroscopy, eds. A. [aubereauand M. Stockburger, (Springer-Verlag, Berlin, 1985), pgs. 170-174.
19. [.C.Mayne and B. Hudson, 3. phys. Chem. 91 (1987) 4438. 20. P.B. Kelly, A. Ruggiero, S. Li, G. Harhay, G.D. Strahan and B. Hudson, in Tenth International Conference on Ranian Spectroscopy, W.L. Peticolas and B. Hudson, editors (University of Oregon, Eugene, 1986) page 20.11-20.12. 21. B. Hudson, Spectroscopy 2 (1987) 33.
FAR ULTRAVIOLET RESONANCE RAMAN SPECTROSCOPY: ULTRAVIOLET REGION
827
NEW CAPABILITY AND APPLICATIONS IN THE VACUUM
Bruce HUDSON Department of Chemistry & Chemical Physics Institute, University of Oregon Eugene, Oregon 97403, United States of America* The development and performance of laser techniques for obtaining resonance Raman spectra in the far ultraviolet region will be described. Examples of spectra with radiation as short as 141.2 nm are presented. The utility of this technique as a method for providing valuable new information about excited electronic states and high energy vibrational transitions is illustrated with several examples. The prospects for extension of this technique to even shorter wavelengths and the generation of tunable radiation in this region will be discussed with emphasis on the use of s-barium borate for harmonic generation. Resonance Raman scattering (or resonance
sities of particular ground electronic state
secondary radiation) has long been recognized as a useful method for obtaining information
vibrational bands. The symmetry and the nature of the atomic motions of these vibra-
concerning excited electronic state potential surfaces. Recent advances in laser technology
tions is usually known with some degree of certainty.
now permit the application of this simple technique using ultraviolet radiation. This allows the examination of highly excited
This technique can also be used to establish the electronic symmetry of an excited state if it results in a transition from the ground
electronic states and excitations of small molecules of theoretical interest. These
state that is forbidden by symmetry for the ground state equilibrium geometry. In
high energy electronic excitations, particularly in small molecules, often result in large changes in the molecular geometry
this case the intensity of the transition must come from the transient displacement of the molecule along non-totally symmetric
along certain coordinates. Sometimes photodissociation or isomerization occurs in the excited
modes of vibration. In the linear vibronic coupling approximation this results in the
state. These features of the excitation, in addition to spectral complexity, may
appearance of characteristic two-quantum transitions of this mode. The symmetry of
make the absorption spectrum diffuse and difficult to interpret, The vibrational Raman spectrum observed under conditions of resonance with such excited states often shows clearly the nature
these modes often determines the symmetry of the excited electronic state. This method has been applied to benzene and its deny46 and butadiene7. atives Another interesting aspect of ultraviolet
of the geometry change in the excited state.~3 This information is relatively easy to interpret
resonance Raman spectroscopy is that highly excited vibrational levels of the ground
because it is obtained in the form of inten-
state are often observed that are not found in normal (off-resonance) Raman spectra
*Research supported by grants from the US National Science Foundation (CHE85-11799) US National Institutes of Health (GM32324) 0022—2313/88/$03.50 ©
Elsevier Science Publishers By.
(North-Holland Physics Publishing Division)
828
B. Hudson
/
Far ultraviolet resonance Roman speciroscopy
813 This occurs when or infra-red spectra. the electronic excitation results in a large
4. L.D. Ziegler and B. Hudson, 3. Chem. Phys. 74 (1981) 232.
geometry change. Because of this effect, new information concerning the ground state poten-
5. D.P. Gerrity, L.D. Ziegler, P.B. Kelly, R. A. Desidenio and B. Hudson, 3. Chem. Phys. 83 (1985) 3209.
tial surface is obtained. This new technique has also been applied to molecules of biological interest.1419
6. L.D. Ziegler and B. Hudson, 3. Chem. Phys. 79 (1983) 1134.
The methodology used to obtain ultraviolet
7. R.R. Chadwick, D.P. Gerrity and B. Hudson, Chem. Phys. Lett. 115 (1985) 24.
radiation for these studies2’20 is based on the generation of harmonics of a high power
8. R.A. Desiderio, D.P. Gerrity and B. Hudson Chem. Phys [ett.115 (1985) 29.
Nd:YAG laser at 532, 355, 266 and 213 nm. The radiation at 532, 355 and 266 nm is suffi-
9. L.D. Ziegler and B. Hudson, 3. Phys. Chem. 88 (1984) 1110.
ciently intense that it can be shifted to shorter wavelengths via stimulated Raman scattening. If hydrogen gas is used as the Raman shifting medium, the new radiation differs
10. L.D. Ziegler, P.B. Kelly and B. Hudson, 3. Chem. Phys. 81 (1984) 6399. 11. P.B. Kelly and B. Hudson, Chem. Phys. Lett. 114 (1985) 451.
from the input by multiples of the vibrational -l frequency of hydrogen, 4155 cm . Thus, for
12. L.D. Ziegler and B. Hudson, 3. Chem. Phys. 79 (1983) 1197.
example, input radiation at 266 nm results in output radiation at 240, 218, 200, 184, 171, 160, 150, 141, 133 nm etc. The shortest
13. R.J. Sension, [.C.Mayne and B. Hudson, 3. Am. Chem. Soc. 109 (1987) 5036.
wavelength used for Raman scattering to date is 141.2 nm.13 The recently developed non-linear optical crystal s-barium borate 21 permits generation of 213 nm radiation with sufficient intensity that stimulated Raman shifting should be possible and even shorter wavelengths can
.
14. B. Hudson and L.C. Mayne in: Biological Applications of Raman Spectroscopy, ed. T.G. Spiro (John Wiley, New York, 1987) pp. 181200. 15. B. Hudson and L.C. Mayne, Meth. 130 (1986) 331.
Enzymol.,
16. [.0.Ziegler, B. Hudson, D.P. Strommen and W.L. Peticolas, Biopolymers 23 (1984) 2067.
be generated. 17. W.L. Kubasek, B. Hudson and W. L. Peticolas, Proc. Nat. Acad. Sci. USA 82 (1985) 451. REFERENCES
18. L.C. Wayne, L.D. Ziegler and B. Hudson, 3. Phys. Chem. 89 (1985) 3395.
1. B. Hudson, Spectroscopy, 1 (1986) 22. 2. B. Hudson, P.8. Kelly, L.D. Ziegler, R.A. Desiderio, D.P. Gerrity, W. Hess and R. Bates in: Advances in Laser Spectroscopy, Volume 3, eds. B.A. Garetz and 3.R. [ombardi, (John Wiley & Sons, New York, 1986) pp. 1-32. 3. B. Hudson in: Time-Resolved Vibrational Spectroscopy, eds. A. [aubereauand M. Stockburger, (Springer-Verlag, Berlin, 1985), pgs. 170-174.
19. [.C.Mayne and B. Hudson, 3. phys. Chem. 91 (1987) 4438. 20. P.B. Kelly, A. Ruggiero, S. Li, G. Harhay, G.D. Strahan and B. Hudson, in Tenth International Conference on Ranian Spectroscopy, W.L. Peticolas and B. Hudson, editors (University of Oregon, Eugene, 1986) page 20.11-20.12. 21. B. Hudson, Spectroscopy 2 (1987) 33.