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POSTDOC AND PHD POSITIONS IN DYNAMICS OF CHEMICAL REACTIONS
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Applications (deadline 30 June 2001) are invited for one PhD position
and three post-doc positions, available starting anytime between
July-December 2001, for theoretical research on the dynamics of
chemical reactions, at the Leiden Institute of Chemistry and Leiden
Observatory of Leiden University, The Netherlands. The research will
be carried out in the framework of a collaboration between the
Theoretical Chemistry group (Dr. G.J. Kroes and Dr. M.C. van Hemert)
and the Astrochemistry group (Prof. E.F. van Dishoeck), with funding
from the Netherlands Organization for Scientific Research, NWO. Two
projects involve gas phase reactions, and two projects involve
molecule-surface reactions taking place on ice
surfaces. These projects are described below.
Applications should be sent by the June 30 deadline to:
Dr. G.J. Kroes, LIC, Gorlaeus Laboratories, P.O. Box 9502, 2300 RA
Leiden, The Netherlands.
FAX: +31-71-5274488, e-mail: [log in to unmask]
Candidates for the PhD position are requested to submit a CV, list of
grades, and arrange for two letters of reference. Candidates for the
postdoc positions are requested to send a CV, publication list, and
arrange for three letters of reference.
More information can be found through
http://rulgla.leidenuniv.nl/main_page.html
and http://www.strw.leidenuniv.nl/~ewine.
PROJECT 1. RADIATIVE ASSOCIATION (PhD student, 4 years)
In radiative association, two atoms or molecules combine to form a
single new molecule by releasing their excess energy through photons.
Radiative association is an essential process for the formation of
molecules at low pressures, such as found in interstellar clouds. An
important example within astrochemistry is the radiative association
of a positively charged carbon ion with molecular hydrogen. This
reaction is assumed to drive the entire carbon chemistry in
interstellar space. For the modelling of this chemistry, accurate
rate coefficients are required.
The time-dependent wave packet method will be used to study the
dynamics and determine rate coefficients for the above-mentioned
reaction. The necessary potential energy surfaces will be computed
using high level ab initio methods, as part of the project. The
central goal of the project is to determine the reaction mechanism,
i.e., the relative importance of purely electronic and vibronic
radiative transitions for the stabilization of the product molecule.
Other goals are to determine the lifetime of the collision complex,
the radiative lifetime of the complex, and the dependence of these
parameters on initial conditions.
Requirements: a Masters (or equivalent) degree in chemistry, physics,
astronomy, or numerical mathematics, with an interest in molecular
quantum mechanics. Experience with numerical methods and computer
programming will be helpful, but is not strictly necessary. For
further information, please contact:
Dr. M.C. van Hemert, email [log in to unmask], or
Dr. G.J. Kroes, email [log in to unmask], or
Prof. E.F. van Dishoeck, email [log in to unmask]
PROJECT 2: QUANTUM DYNAMICS OF A FOUR-ATOM REACTION (postdoc)
The study of four-atom reactions of the type AB + CD -> ABC + D is of
tremendous interest to chemistry. These reactions represent the
smallest system in which a molecule reacts with a molecule. The
development of accurate methods for studying such reactions is of
long term interest to the theoretical treatment of reactions of
larger molecules. The reaction of OH with CO is important to
atmospheric chemistry as well as astrochemistry, and is a prototype
of a reaction that proceeds via the formation of a long-lived
collision complex. According to quantum mechanics, such complexes can
only exist in specific metastable states, and a central goal of the
project is to determine how these states affect the reactivity. Other
goals are to determine the influence of spin-orbit coupling, and of
the initial vibrational state of the CO reactant, on the reaction.
In the project, the OH + CO reaction is studied using the
time-dependent wave packet method. The motion in all molecular
degreesof freedom will be modelled quantum mechanically with
essentially no approximations. Part of the calculations will be done
using available potential energy surfaces. The development of new
potential energy surfaces using high level ab initio methods is also
part of the project.
Term of appointment: The initial appointment is for one year, with
funding available for extension up to 3.5 years in total.
Required: a PhD in Chemistry, Physics, Astronomy, or Numerical
Mathematics, with an interest in molecular quantum mechanics.
Experience with numerical methods and computer programming will be
helpful, but is not strictly necessary. For further information,
please contact:
Dr. G.J. Kroes, email [log in to unmask], or
Dr. M.C. van Hemert, email [log in to unmask]
PROJECT 3. REACTIONS ON INTERSTELLAR ICE SURFACES (post-doc)
In dense interstellar clouds, small dust particles (consisting of
~0.1 micron silicates) are covered by ice mantles consisting of H2O,
CO, CO2, CH4 and other species, at a temperature of ~10 K. Recent
observations with the Infrared Space Observatory (ISO) show that
larger molecules such as H2CO, CH3OH, and HCOOH may be present as
well. The current assumption is that these larger molecules form by
hydrogenation and oxidation reactions of smaller molecules such as
CO, which take place at the ice surface or in the ice mantle.
Laboratory experiments on these reactions are being started at the
Sackler
Laboratory at Leiden Observatory.
In the project, the above mentioned reactions are studied by first
performing molecular dynamics simulations to "make" particles of
amorphous ice in the computer. Next, the reaction of, e.g., CO with H
on the surface of such particles will be modelled using quantum
transition state theory. In addition, classical trajectory
calculations will be performed to obtain mechanistic insights into
the most important pathways, and to visualize these reactions. The
central goal is to determine which chemical reactions can occur on
interstellar ices, and to determine the dominant reaction mechanisms.
Term of appointment: The initial appointment is for one year, with
funding available for extension up to 3 years in total.
Required: a PhD in Chemistry, Physics, or Astronomy, with an interest
in molecular quantum mechanics. Experience with numerical methods and
computer programming will be helpful, but is not strictly necessary.
For further information, please contact:
Dr. G.J. Kroes, email [log in to unmask], or
Prof. E.F. van Dishoeck, email [log in to unmask]
PROJECT 4. REACTIONS ON ATMOSPHERIC ICE PARTICLES (postdoc)
Reactions of chlorine-containing molecules at surfaces of ice
particles that are present in so-called polar stratospheric clouds
play an essential role in causing the ozone hole. An example of this
type of reaction is that of chloronitrate with water to form nitric
acid and ClOH. Important questions regarding this and similar
reactions concern the role of the surface in the reaction mechanism.
A key question is whether the transfer of the hydrogen atom, which is
required in this and most other important reactions, takes place
directly from one reactant to the other reactant molecule, or whether
it occurs through the ice surface.
In the project, several reactions of chlorine- and bromine-containing
molecules on plain ice surfaces or nitric acid trihydrate (NAT)
surfaces will be studied, with the use of quantum transition state
theory. The goal of the project is to arrive at a detailed
understanding of the mechanisms of the important reactions, and to
obtain an order of magnitude estimate of their rates.
Term of appointment: The initial appointment is for one year, with
funding available for extension up to 2.8 years in total.
Required: a Ph.D. in Chemistry, Physics, or Astronomy, with an
interest in molecular quantum mechanics. Experience with numerical
methods and computer programming will be helpful, but is not strictly
necessary. For further information, please contact:
Dr. G.J. Kroes, email [log in to unmask], or
Dr. M.C. van Hemert, email [log in to unmask]
--
G.J.Kroes ([log in to unmask], or
[log in to unmask])
LIC
Gorlaeus Laboratoria
Universiteit Leiden
Postbus 9502
2300 RA Leiden
The Netherlands
(tel.+31 71 527 4396, Fax +31 71 527 4488)
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