Infrared multiple photon absorption is known to be observed in some triatomic and most polyatomic
molecules. When the number of absorbed photons is high enough the process leads to photodissociation
and excess energy is released as vibrational, rotational and translational energy in the electronic ground
state of the fragments. The contribution of these energies is determined by standard methods, that include
laser induced fluorescence, LIF, and time-resolved Fourier transform spectroscopy, TR-FTS. Examples
of selected determinations are shown.Once produced, identified and characterized, the kinetic behaviour of the transients with selected
reactants can be studied. In particular, removal rate constants of substituted carbenes, in specific
vibrational and electronic states, by atoms, olefins and simple molecules are mentioned.

F.  Casta&#241;o

A. Ortiz De Z&#225;rate

J. A. Fern&#225;ndez

M. N. S&#225;nchez Rayo

Kinetic and Spectroscopic Studies of Transient Species Prepared by
Irmpd

The modification of photodissociation mechanisms of small molecules by adsorption on a solid or by
condensation is briefly reviewed. The coupling to the surroundings leads to quenching of easily
delocalizable primary excitations so that only strongly localized channels show up in dissociation (detected
by photodesorption, i.e. by the appearance of fragments in the gas phase). In reverse, fast direct
dissociation channels will be less in need of such localization and will be preferred over slow channels.
Investigation of dissociation induced by core excitations or core shake-ups introduces an internal time
mark&#8212;core life time&#8212;to which reaction time can be compared. The example of small molecules, such as
CO or NO, adsorbed on transition metal surfaces is surveyed, in which complex multiple excitations
predominate in dissociation. Recent results on the core-induced dissociation of condensed hydrogenic
molecules such as water, ammonia, and benzene have shown the existence of preferential dissociation
channels in the core-to-bound region. It is argued that these dissociation processes are at least competitive
with core decay; they are termed ultrafast. It appears that they should also exist in the free
molecules.

Dietrich  Menzel

Selective Photodissociation of Condensed and Adsorbed Small
Molecules by Specific Core-to-Bound Excitations: Evidence for
Ultrafast Dissociation Channels

Two techniques for rotational analysis of the nd<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>&#x2190;</mml:mo><mml:mn>1</mml:mn><mml:msub><mml:mi>b</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math> Rydberg spectra of H2O and D2O are discussed&#8212;a
Coriolis coupled asymmetric top model for the room temperature 3d<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>&#x2190;</mml:mo><mml:mn>1</mml:mn><mml:msub><mml:mi>b</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math> cluster, and an extension of
multichannel quantum defect theory to asymmetric tops, which is applied to recent jet cooled photoionization
spectra of the nd<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>&#x2190;</mml:mo><mml:mn>1</mml:mn><mml:msub><mml:mi>b</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math> series converging to the (100) vibrational levels of H2O+ and D2O+. The
quantum defects obtained by the two methods are in good agreement and new ionization limits to the
(100) series are derived: IP(100) &#61; 104985(2) cm&#8722;1 for H2O and 104262(1) cm&#8722;1 for D2O.

M. S.  Child

R. D. Gilbert

Ch.  Jungen

Rotational Analysis of the Rydberg Spectrum of Water

A.  Aguilar-Navarro

J.  de Andr&#233;s-Llopis

Preface

Dynamics studies of the electronic excited states of some small molecules have been carried out. Collision
free lifetimes of different rotational and vibrational levels of the A and B states of 130Te2 and 80Se2 have
been obtained. Predissociation studies of the B states of the Br2 and Cl2 molecules have been carried out.
Results are discussed in terms of perturbation or predissociation effects.

E.  Mart&#237;nez

M. R. L&#243;pez

F.  Basterrechea

P.  Puyuelo

Dynamics of Quantum Selected Levels of Electronic Excited States of
Small Molecules

Photofragmentation spectroscopy&#8212;the study of &#8220;half collisions&#8221; with polarized light of subdoppler line
width&#8212;opens a window to look into the structure of molecules. The energy partitioning among the
particular degrees of freedom of the products of the fragmentation reaction is described by the scalar
properties, the direction and magnitude of a particular type of motion is described by the vector
properties. The measurement of the scalar and vector properties allows a pictorial view of the intermediate
state. The forces which make the fragments fly apart or rotate and vibrate can be &#8220;seen&#8221; from the line
shapes. Information on the unstable intermediate state is gained from the stable fragments long after the
dissociation of the parent molecule. In particular, information on the &#8220;lifetime&#8221; of the intermediate on a
femtosecond time scale can be obtained.A number of molecules, mainly three and four atomic, have been studied by this technique. Hydrogen
peroxide has shown up as a textbook example. A complete analysis was possible including not only
correlation of different types of fragment motion but also a correlation of the two coincident particles
formed from the same parent molecule. The experimental results are in full agreement with recent
calculations of the dynamics of the fragmentation on newly obtained potential energy surfaces. Hydrogen
peroxide shows a strong dependence of its potential energy on the dihedral angle in the two electronic
states amenable to laser excitation. This experiment further demonstrates that an analysis is also possible
if two states are excited simultaneously.Another good example is the fragmentation of hydrazoic acid for which also coincident pair correlation
has been treated. Here again the results agree excellently with a qualitative picture which can be drawn
from recently calculated ab initio potential energy surfaces. The HN3 example is much more complicated
than the former one due to its higher structured upper potential energy surface. Strong rotational
excitation is observed in the N2 fragment leaving the NH fragment rotationally cold.The treatment of vector correlations in molecular photofragmentation is a powerful tool for the study of
the dynamics of molecular dissociation reactions.

F. J. Comes

Vector Correlations in Molecular Photofragmentations

The combination of high resolution laser spectroscopy in collimated cold molecular beams with mass
selective detection allows investigations of rotationally resolved molecular spectra of selected molecular
species in the presence of molecules with overlapping absorption spectra. This is illustrated by some
examples, such as the isotope selective spectroscopy of Ag2&#8211;dimers or the sub-Doppler spectroscopy of
Na3 in supersonic beam with a broad mass distribution of different clusters. Time resolved laser
spectroscopy of excited states of alkali molecules, perturbed by bound dark states or by repulsive states,
yields information about singlet&#8211;triplet mixing and predissociation rates.

V.  Beutel

H.-J.  B&#246;hm

W.  Demtr&#246;der

H.-A.  Eckel

J.  Gress

M.  Kuhn

A.  Sasso

High Resolution Laser Spectroscopy of Small Molecules and Clusters

The determination of the state of the excited photofragments gives informations on couplings occurring at
large internuclear distance. The H(1s) + H(n &#61; 2) photodissociation of H2 is well explained with a
transition probability between the B and B&#39; continua occurring at r &#8776; 15a0. The H(1s) + H(n &#61; 3)
photodissociation of H2 presents unsolved questions.

M.  Glass-Maujean

J. A. Beswick

H.  Frohlich

Photodissociation and Large Internuclear Distance Dynamics

The ionization event in the He(23S)&#8211;H2 collision system at the collision energy of 80 me V is described by a
modified version of the trajectory surface leaking method. The approach is found to yield an improved
picture of the event which is consistent with Penning electron spectra measurements.

J.  Vojt&#237;k

Theoretical Description of The He(23S)&#8211;H2 Autoionising Collision
System

The use of synchroton radiation combined with TPEPICO experiments to study the photoionization
dynamics of molecules at Orsay&#39;s synchroton radiation facility is discussed. The initial state preparation by
Threshold Photoelectron Spectroscopy and final state-mass and internal energy spectroscopy by time of
flight analysis of photoelectrons as well as ions in coincidence with threshold electrons is illustrated by the
TPES of HCl, the TOF TPES of O2 and the TPEPICO spectra of NO+ fragments from the decay of state
selected N2O+ ions.

Paul Marie Guyon

Photoionization Dynamics of Small Molecules With Synchrotron
Radiation: State Preparation by Pepico and Tpepico

About this journal

Journal profile

Meet the editorial board

Editor spotlight

Submit your proposal

Do you think there is an emerging area of research that really needs to be highlighted? Or an existing research area that has been overlooked or would benefit from deeper investigation? Raise the profile of a research area by leading a Special Issue.

Special Issues

title

https://images.hindawi.com/journals/lc/lc.banner.jpg

twitter:card

twitter:site

twitter:title

twitter:url

twitter:image

Laser Chemistry | Hindawi

Laser Chemistry

This Issue is now open for submissions.
Papers are published upon acceptance, regardless of the Special Issue publication date.

Call for papers

A. Aguilar-Navarro

J. D<small.letters>e</small.letters> Andrés-Llopis