where helium buffer gas is present another issue to consider is cooling by collisions
which can result in complicated power dependencies.
While action spectroscopy of positive ions requires dissociation, electron loss
can be the action channel for negative ions. This circumvents the problem
associated with spectroscopy of large biomolecular ions where one photon hardly
changes the internal energy per degree of freedom. Prompt dissociation of large
molecular ions occurring on the excited-state potential energy surface can be
another way to identify that photon absorption has occurred, but this is of course
very much limited to certain ions and is a less general approach. These fast
dissociation processes can be explored by photoexcitation of ions in an electric
field as fragment ions formed in the field region will have different kinetic energies
than those formed outside. Ion-beam depletion experiments with storage rings also
shed light on the importance of such fast dissociation processes.
When it comes to fluorescence experiments, ion traps are the instruments of
choice. The difficulty is to detect enough emitted light but recent developments
have shown that this is indeed possible.
Finally, electronic spectroscopy of cold biomolecular ions is in its infancy but is
likely to be an intense research field within the next years, particularly due to the
construction of new state-of-the-art instruments.
References
1. Fenn, J.B., Mann, M., Meng, C.K., Wong, S.F., Whitehouse, C.M.: Electrospray ionization for
mass-spectrometry of large biomolecules. Science 246, 64–71 (1989)
2. Karas, M., Bachmann, D., Hillenkamp, F.: Influence of the wavelength in high-irradiance
ultraviolet-laser desorption mass-spectrometry of organic-molecules. Anal. Chem. 57,
2935–2939 (1985)
3. Tanaka, K., Waki, H., Ido, Y., Akita, S., Yoshida, Y., Yoshida, T., Matsuo, T.: Protein and
polymer analyses up to m/z 100 000 by laser ionization time-of-flight mass spectrometry.
Rapid Commun. Mass Spectrom. 2, 151–153 (1988)
4. Panja, S., Kadhane, U., Andersen, J.U., Holm, A.I.S., Hvelplund, P., Kirketerp, M.B.S.,
Brøndsted Nielsen, S., Støchkel, K., Compton, R.N., Forster, J.S., Kilsa, K., Nielsen, M.B.:
Dianions of 7,7,8,8-tetracyano-p-quinodimethane and perfluorinated tetracyanoquinodimethane: Information on excited states from lifetime measurements in an electrostatic
storage ring and optical absorption spectroscopy. J. Chem. Phys. 127, 124301 (2007)
5. Støchkel, K., Wyer, J.A., Kirketerp, M.B.S., Brøndsted Nielsen, S.: Laser pump-probe
experiments on microsecond to millisecond timescales at an electrostatic ion storage ring:
triplet-triplet absorption by protoporphyrin-IX anions. J. Am. Soc. Mass Spectrom. 21,
1884–1888 (2010)
6. Andersen, J.U., Cederquist, H., Forster, J.S., Huber, B.A., Hvelplund, P., Jensen, J., Liu, B.,
Manil, B., Maunoury, L., Brøndsted Nielsen, S., Pedersen, U.V., Schmidt, H.T., Tomita, S.,
Zettergren, H.: Power-law decay of collisionally excited amino acids and quenching by
radiative cooling. Eur. Phys. J. D 25, 139–148 (2003)
7. Rosenstock, H.M., Wallenstein, M.B., Wahrhaftig, A.L., Eyring, H.: Absolute rate theory for
isolated systems and the mass spectra of polyatomic molecules. Proc. Natl. Acad. Sci. USA.
38, 667–678 (1952)
42
J.A. Wyer
which can result in complicated power dependencies.
While action spectroscopy of positive ions requires dissociation, electron loss
can be the action channel for negative ions. This circumvents the problem
associated with spectroscopy of large biomolecular ions where one photon hardly
changes the internal energy per degree of freedom. Prompt dissociation of large
molecular ions occurring on the excited-state potential energy surface can be
another way to identify that photon absorption has occurred, but this is of course
very much limited to certain ions and is a less general approach. These fast
dissociation processes can be explored by photoexcitation of ions in an electric
field as fragment ions formed in the field region will have different kinetic energies
than those formed outside. Ion-beam depletion experiments with storage rings also
shed light on the importance of such fast dissociation processes.
When it comes to fluorescence experiments, ion traps are the instruments of
choice. The difficulty is to detect enough emitted light but recent developments
have shown that this is indeed possible.
Finally, electronic spectroscopy of cold biomolecular ions is in its infancy but is
likely to be an intense research field within the next years, particularly due to the
construction of new state-of-the-art instruments.
References
1. Fenn, J.B., Mann, M., Meng, C.K., Wong, S.F., Whitehouse, C.M.: Electrospray ionization for
mass-spectrometry of large biomolecules. Science 246, 64–71 (1989)
2. Karas, M., Bachmann, D., Hillenkamp, F.: Influence of the wavelength in high-irradiance
ultraviolet-laser desorption mass-spectrometry of organic-molecules. Anal. Chem. 57,
2935–2939 (1985)
3. Tanaka, K., Waki, H., Ido, Y., Akita, S., Yoshida, Y., Yoshida, T., Matsuo, T.: Protein and
polymer analyses up to m/z 100 000 by laser ionization time-of-flight mass spectrometry.
Rapid Commun. Mass Spectrom. 2, 151–153 (1988)
4. Panja, S., Kadhane, U., Andersen, J.U., Holm, A.I.S., Hvelplund, P., Kirketerp, M.B.S.,
Brøndsted Nielsen, S., Støchkel, K., Compton, R.N., Forster, J.S., Kilsa, K., Nielsen, M.B.:
Dianions of 7,7,8,8-tetracyano-p-quinodimethane and perfluorinated tetracyanoquinodimethane: Information on excited states from lifetime measurements in an electrostatic
storage ring and optical absorption spectroscopy. J. Chem. Phys. 127, 124301 (2007)
5. Støchkel, K., Wyer, J.A., Kirketerp, M.B.S., Brøndsted Nielsen, S.: Laser pump-probe
experiments on microsecond to millisecond timescales at an electrostatic ion storage ring:
triplet-triplet absorption by protoporphyrin-IX anions. J. Am. Soc. Mass Spectrom. 21,
1884–1888 (2010)
6. Andersen, J.U., Cederquist, H., Forster, J.S., Huber, B.A., Hvelplund, P., Jensen, J., Liu, B.,
Manil, B., Maunoury, L., Brøndsted Nielsen, S., Pedersen, U.V., Schmidt, H.T., Tomita, S.,
Zettergren, H.: Power-law decay of collisionally excited amino acids and quenching by
radiative cooling. Eur. Phys. J. D 25, 139–148 (2003)
7. Rosenstock, H.M., Wallenstein, M.B., Wahrhaftig, A.L., Eyring, H.: Absolute rate theory for
isolated systems and the mass spectra of polyatomic molecules. Proc. Natl. Acad. Sci. USA.
38, 667–678 (1952)
42
J.A. Wyer