3 Ultrafast Dynamics of Hydrogen Atoms in Hydrocarbon Molecules
59
singly charged and/or doubly charged parent ions to the triply charged species. This
is because the enhancement of the ionization is expected to occur when the C–C
internuclear distance becomes approximately twice as large as the equilibrium internuclear distance, and consequently, by the time when the ionization to the triply
charged stage occurs, the distance between the heavy moieties is too far for hydrogen atoms to migrate further. Considering that three-body decomposition proceeds
immediately after triply charged precursor ions are produced, the probability of hydrogen migration to occur after the triple ionization should be extremely low.
In addition, a different type of three-body decomposition processes in which two
light ion species such as H + and H
+
2 are ejected are identified for methylacetylene
and methyl-d 3 -acetylene. From the momentum correlation maps for methylacetylene, it was revealed that the three-body decomposition proceeds in a concerted
manner so that H + and H
+
2 are ejected almost simultaneously. It was also shown
that events in which H + starts to leave earlier than H
+
2 and those in which H
+
2 starts
to leave earlier than H + coexist.
As has been shown in the present chapter as well as in our previous studies, the
motions of at least two or three hydrogen atoms need to be considered simultaneously for describing hydrogen migration processes even when apparently one proton moves. The migration, exchange, and scrambling processes of hydrogen atoms
occurring within a very short period of time can be characteristic phenomena commonly observed in hydrocarbon molecules when they are exposed to an intense laser
field, and this highly correlated ultrafast motion of hydrogen atoms may better be
treated by a theoretical method beyond Born-Oppenheimer approximation such as
that developed by our group [28, 29] in which protons are represented by multiplecentered wave functions like electrons in a molecule.
Acknowledgements We thank Prof. Huailiang Xu (Jilin University) for conducting measurements and his variable comments. The present research was supported by the following three
grants from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan;
the Grant-in-Aid for Specially Promoted Research on Ultrafast Hydrogen Migration (#19002006),
the Grant-in-Aid for Global COE Program for Chemistry Innovation and Special Coordination
Funds for Promoting Science and Technology.
References
1. K. Yamanouchi, S.L. Chin, P. Agostini, G. Ferrante (eds.), Progress in Ultrafast Intense Laser
Science I–VI (Springer, Heidelberg, 2006–2010)
2. J.H. Posthumus, Rep. Prog. Phys. 67, 623 (2004)
3. A. Hishikawa, H. Hasegawa, K. Yamanouchi, Phys. Scr. T 110, 108 (2004)
4. A. Hishikawa, H. Hasegawa, K. Yamanouchi, J. Electron Spectrosc. Relat. Phenom. 141, 195
(2004)
5. A.S. Alnaser, I. Litvinyuk, T. Osipov, B. Ulrich, A. Landers, E. Wells, C.M. Maharjan, P.
Ranitovic, I. Bochareva, D. Ray, J. Phys. B, At. Mol. Opt. Phys. 39, S485 (2006)
6. T. Okino, Y. Furukawa, P. Liu, T. Ichikawa, R. Itakura, K. Hoshina, K. Yamanouchi, H.
Nakano, Chem. Phys. Lett. 423, 220 (2006)
7. P. Liu, T. Okino, Y. Furukawa, T. Ichikawa, R. Itakura, K. Hoshina, K. Yamanouchi, H.
Nakano, Chem. Phys. Lett. 423, 187 (2006)
59
singly charged and/or doubly charged parent ions to the triply charged species. This
is because the enhancement of the ionization is expected to occur when the C–C
internuclear distance becomes approximately twice as large as the equilibrium internuclear distance, and consequently, by the time when the ionization to the triply
charged stage occurs, the distance between the heavy moieties is too far for hydrogen atoms to migrate further. Considering that three-body decomposition proceeds
immediately after triply charged precursor ions are produced, the probability of hydrogen migration to occur after the triple ionization should be extremely low.
In addition, a different type of three-body decomposition processes in which two
light ion species such as H + and H
+
2 are ejected are identified for methylacetylene
and methyl-d 3 -acetylene. From the momentum correlation maps for methylacetylene, it was revealed that the three-body decomposition proceeds in a concerted
manner so that H + and H
+
2 are ejected almost simultaneously. It was also shown
that events in which H + starts to leave earlier than H
+
2 and those in which H
+
2 starts
to leave earlier than H + coexist.
As has been shown in the present chapter as well as in our previous studies, the
motions of at least two or three hydrogen atoms need to be considered simultaneously for describing hydrogen migration processes even when apparently one proton moves. The migration, exchange, and scrambling processes of hydrogen atoms
occurring within a very short period of time can be characteristic phenomena commonly observed in hydrocarbon molecules when they are exposed to an intense laser
field, and this highly correlated ultrafast motion of hydrogen atoms may better be
treated by a theoretical method beyond Born-Oppenheimer approximation such as
that developed by our group [28, 29] in which protons are represented by multiplecentered wave functions like electrons in a molecule.
Acknowledgements We thank Prof. Huailiang Xu (Jilin University) for conducting measurements and his variable comments. The present research was supported by the following three
grants from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan;
the Grant-in-Aid for Specially Promoted Research on Ultrafast Hydrogen Migration (#19002006),
the Grant-in-Aid for Global COE Program for Chemistry Innovation and Special Coordination
Funds for Promoting Science and Technology.
References
1. K. Yamanouchi, S.L. Chin, P. Agostini, G. Ferrante (eds.), Progress in Ultrafast Intense Laser
Science I–VI (Springer, Heidelberg, 2006–2010)
2. J.H. Posthumus, Rep. Prog. Phys. 67, 623 (2004)
3. A. Hishikawa, H. Hasegawa, K. Yamanouchi, Phys. Scr. T 110, 108 (2004)
4. A. Hishikawa, H. Hasegawa, K. Yamanouchi, J. Electron Spectrosc. Relat. Phenom. 141, 195
(2004)
5. A.S. Alnaser, I. Litvinyuk, T. Osipov, B. Ulrich, A. Landers, E. Wells, C.M. Maharjan, P.
Ranitovic, I. Bochareva, D. Ray, J. Phys. B, At. Mol. Opt. Phys. 39, S485 (2006)
6. T. Okino, Y. Furukawa, P. Liu, T. Ichikawa, R. Itakura, K. Hoshina, K. Yamanouchi, H.
Nakano, Chem. Phys. Lett. 423, 220 (2006)
7. P. Liu, T. Okino, Y. Furukawa, T. Ichikawa, R. Itakura, K. Hoshina, K. Yamanouchi, H.
Nakano, Chem. Phys. Lett. 423, 187 (2006)