Chapter 4
Femtosecond Photodissociation Dynamics
by Velocity Map Imaging. The Methyl Iodide
Case
Rebeca de Nalda, Luis Rubio-Lago, Vincent Loriot, and Luis Bañares
Abstract The introduction of time-resolved measurements in the femtosecond
time-scale using velocity map imaging techniques of charged particles (ions
and photoelectrons) in combination with resonant multiphoton ionization of the
fragments for the study of the photodissociation dynamics of small polyatomic
molecules is reviewed. A typical experiment consists of the measurement of a sequence of images, whose analysis requires in most cases sophisticated multidimensional fitting methods to extract all the relevant time-resolved information contained
in the images. In particular, the application of these techniques to the study of the
direct photodissociation (A band) and electronic predissociation (B band) of methyl
iodide along with the detection and characterization of transient species and the
study of cluster dissociation, as a case example for femtosecond velocity map imaging, are presented and discussed.
4.1 Introduction
In the last decades, the field of laser photochemistry has reached an important technical maturity, due to the development of versatile laser sources and powerful detection techniques. One of the followed directions has aimed to explore dynamics
directly in the time scales of chemical molecular processes, which are typically in
the femtosecond to picosecond range. Understanding the time required for a process
to take place—if such concept is suitable of a precise definition within the realm of
the microscopic world—implies the possibility of either measuring, or externally
inducing, the start and finish moments of the process. In standard two-body reaction
dynamics, the definition of the start of the reaction is arbitrary, given the long-range
potentials involved in a chemical reaction, and this is complicated by the fact that
R. de Nalda · V. Loriot
Instituto de Química Física Rocasolano, CSIC, C/ Serrano, 119, 28006 Madrid, Spain
L. Rubio-Lago · V. Loriot · L. Bañares (B)
Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de
Madrid, 28040 Madrid, Spain
e-mail: banares@quim.ucm.es
R. de Nalda, L. Bañares (eds.), Ultrafast Phenomena in Molecular Sciences,
Springer Series in Chemical Physics 107, DOI 10.1007/978-3-319-02051-8_4,
© Springer International Publishing Switzerland 2014
61
Femtosecond Photodissociation Dynamics
by Velocity Map Imaging. The Methyl Iodide
Case
Rebeca de Nalda, Luis Rubio-Lago, Vincent Loriot, and Luis Bañares
Abstract The introduction of time-resolved measurements in the femtosecond
time-scale using velocity map imaging techniques of charged particles (ions
and photoelectrons) in combination with resonant multiphoton ionization of the
fragments for the study of the photodissociation dynamics of small polyatomic
molecules is reviewed. A typical experiment consists of the measurement of a sequence of images, whose analysis requires in most cases sophisticated multidimensional fitting methods to extract all the relevant time-resolved information contained
in the images. In particular, the application of these techniques to the study of the
direct photodissociation (A band) and electronic predissociation (B band) of methyl
iodide along with the detection and characterization of transient species and the
study of cluster dissociation, as a case example for femtosecond velocity map imaging, are presented and discussed.
4.1 Introduction
In the last decades, the field of laser photochemistry has reached an important technical maturity, due to the development of versatile laser sources and powerful detection techniques. One of the followed directions has aimed to explore dynamics
directly in the time scales of chemical molecular processes, which are typically in
the femtosecond to picosecond range. Understanding the time required for a process
to take place—if such concept is suitable of a precise definition within the realm of
the microscopic world—implies the possibility of either measuring, or externally
inducing, the start and finish moments of the process. In standard two-body reaction
dynamics, the definition of the start of the reaction is arbitrary, given the long-range
potentials involved in a chemical reaction, and this is complicated by the fact that
R. de Nalda · V. Loriot
Instituto de Química Física Rocasolano, CSIC, C/ Serrano, 119, 28006 Madrid, Spain
L. Rubio-Lago · V. Loriot · L. Bañares (B)
Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de
Madrid, 28040 Madrid, Spain
e-mail: banares@quim.ucm.es
R. de Nalda, L. Bañares (eds.), Ultrafast Phenomena in Molecular Sciences,
Springer Series in Chemical Physics 107, DOI 10.1007/978-3-319-02051-8_4,
© Springer International Publishing Switzerland 2014
61