Femtosecond time-resolved imaging of bimolecular reactions using cold helium nanodroplets

Applications are invited for a PhD fellowship/scholarship at Graduate School of Science and Technology, Aarhus University, Denmark, within the Chemistry or Nanoscience programme. The position is available from 1 November 2018 or later.

Femtosecond time-resolved imaging of bimolecular reactions using cold helium nanodroplets

Research area and project description:
The scientific goal of this PhD project is to image molecules with femtosecond (fs) time resolution during fundamental bimolecular reactions. The goal will be achieved by applying fs time-resolved imaging methods to molecular complexes, sharply oriented in space, formed inside helium nanodroplets. 

As a unique approach molecules will be studied inside helium nanodroplets. The helium droplets are created by expanding a cryogenically cooled, high pressure gas of helium into vacuum. They consist of about 10,000 He atoms, have a diameter of ~ 10 nm and a temperature of 0.4 K. The droplets move with a few hundred meters per second and when they pass a doping cell, containing a gas of molecules, they can pick up one or several molecules. The pressure of the gas determines how many molecules each droplet pick up. Thereby, it becomes possible to study either single molecules, using a low doping cell pressure, or dimers (or larger oligomers) of molecules, using a higher doping cell pressure, since two (or more) molecules inside a droplet will bond due to intermolecular interactions. It is also possible to form hetero-dimers by using two consecutive doping cells containing different molecular gases.

To study bimolecular reactions a precursor consisting of two reagent molecules, weakly bonded in a well-defined, yet non-reactive geometry will be made. Experimentally, this will be realized in the form of a molecular dimer created inside the He droplets. The reaction will be initiated by selectively photoexciting one of the reagents by a femtosecond (fs) pump pulse and imaged as a function of time by a delayed fs probe pulse through Coulomb explosion or single-ionization.

The project will aim at studying a range of fundamental photoinduced reactions. One concerns photoinduced cycloadditions, which are central to a range of reactions in organic synthesis and biology. The archetypical reaction is the dimerization of (derivatives) of ethylene (C2H4) to (substituted) cyclobutane by p-p* photoexcitation. One objective may be the photodimerization of 2-butene to 1,2,3,4, tetramethylcyclobutane – a reaction long known to occur when liquid 2-butene is irradiated by UV light around 229 nm. The initial goal is to observe the cyclobutane adduct and how it kinematically competes against photo-fragmentation. We will try to image directly how the geometry changes during the reaction using laser-induced Coulomb explosion. It may be necessary to halogenate the reagents to provide marker ions for the structure determination via Coulomb explosion.

Another goal is to study the photodimerization of nucleobases. When UV light from the sun hits human tissue it can induce covalent bonding between two adjacent thymine or cytosine nucleobases in one part of the strand of a DNA molecule. This dimerization disrupts the hydrogen-bonding to the nucleobases on the opposing strand and thus destroys part of the base-pairing which leads to a loss of the function of the DNA molecule. The effect is believed to be the primary cause of skin cancer in humans. We plan on exploring the atomistic foundation for the nucleobase dimerization using UV excitation with a pump pulse and an (intense) probe pulse to follow the evolution – possibly by Coulomb explosion. Other processes to be studied include charge transfer reactions.

Qualifications and specific competences:
Bachelor or Master degree in Physics, Chemistry or Nanoscience.

Place of Employment and Place of Work:
The place of employment is Aarhus University, and the place of work is Femtolab at the Department of Chemistry, Langelandsgade 140, 8000 Aarhus C, Denmark. 

Applicants seeking further information are invited to contact:

Professor Henrik Stapelfeldt, e-mail: henriks@chem.au.dk

Application procedures

Before you apply

Information and attachments:

Please be aware that you must have all relevant appendices, attachments, addresses for referees, etc. ready when you apply, as the entire application must be uploaded to the system in one go.

Documentation of language skills:

The English language requirement at Graduates School of Science and Technology is comparable to an “English B level” in the Danish upper secondary school (“gymnasium”).

English language qualifications comparable to an “English B level” is documented by one of the following tests:

  • TOEFL test, minimum score: 560 (paper-based test) or 83 (internet-based test). The paper-based test must have a “total score”. From August call 2019, GSST no longer accepts the paper-based test.
    Aarhus University does not accept the TOEFL ITP test. Aarhus University’s TOEFL code is 8935. You must request that the test centre send your test results to Aarhus University, in order to enable verification of your test results.
  • IELTS (academic) test, minimum average score: 6.5 points
  • Cambridge English Language Assessment:
    Cambridge Certificate of Proficiency (CPE)
    Cambridge English: Certificate of Advanced English with grade A,B or C (CAE)
    Cambridge English: First Certificate  with grade A (FCE)

When to take the test and how to upload the documentation:
The test result must not be more than two years old at the time of application.

The English language test should be taken before applying for admission and uploaded under “language skills documentation” in the online application form.

It is possible to apply for admission before you have taken the test. In this case documentation stating that you have signed up for a test (please state expected submission date) must be uploaded. If the test result is not part of the original application the test result is to be sent to sphd@psys.au.dk no later than one month after the application deadline.

The following applicants are exempted from documenting their English qualifications/taking a test:

  • Applicants with citizenship from the following countries: Australia, Canada, Ireland, New Zealand, United Kingdom, United States, or one of the Nordic countries (Denmark, Finland, Iceland, Norway or Sweden).
  • Applicants with a Bachelor’s or Master’s programme completed in Australia, Canada, Ireland, New Zealand, United Kingdom, or United States. In this case, please upload your Bachelor’s or Master’s diploma under the section ”Language skills documentation”.
  • Applicants with a Bachelor’s or Master’s programme completed at Aarhus University for which the requirement was English B level at the time of admission. In this case, please upload your Bachelor’s or Master’s diploma under the section” Language skills documentation”.
  • Applicants able to document that English was the language of instruction during the whole period of their Bachelor’s and/or Master’s programme. This must be documented by uploading an official document from the institution stating this under “language skills documentation”. The onus is on the applicant to provide this information as GSST will not pursue information regarding language of instruction for any programmes or institutions.

The programme committee may request further information or invite the applicant to attend an interview.

How to apply:

1)      Find the application form:
Go to http://talent.au.dk/phd/scienceandtechnology/opencalls/
Choose August 2018 Call with deadline 1 August 2018 at 11.59 PM MET.
You will be directed to the call, and must choose the programme 'Chemistry' or 'Nanoscience' depending on your educational background and type of project.

2)      Fill in the following information:

  • Personal information
  • Academic background
  • Admission
  • Financing (if any)
  • Study: In the dropdown menu you must choose the project: "Femtosecond time-resolved imaging of bimolecular reactions using cold helium nanodroplets"
  • Source (how you found out about the call)

Next to some of the information fields you will find a number. Click on the number to get further directions on how to fill in the information field/what information is needed.


3)      Application attachments:
Please be aware that you cannot submit the application if one or several of these documents have not been uploaded.

If you wish to upload more than one document under each section, you must scan/merge all documents into one large PDF file and upload this. Please note that we reserve the right to remove scientific papers, large reports, theses and the like. Instead you can indicate a URL where the information is available.

Please note that all information in the application must be in Danish or English.

As a minimum all applications must include (pdf-files only, max. 20 MB, no zip):

  • One reference (template for references)
  • Curriculum vitae,
  • Motivation (max. 1 page)
  • Transcripts and diploma(s)
  • Project description (½-4 pages). For technical reasons, you must upload a project description. When - as here - you apply for a specific project, please simply copy the project description above, and upload it as a PDF in the application. If you wish to, you can indicate an URL where further information can be found. Please note that we reserve the right to remove scientific papers, large reports, theses and the like.
  • Documentation of language skills if required.

After submission of the application, you will receive a confirmation e-mail with an application ID, you should use for reference if needed. The e-mail will also include a link to the application – GSST urges you to check that all mandatory data, marked with an asterisk (*), is registered correctly and all attached files are readable. In case of significant errors, you should reply to the confirmation e-mail with the correct details before the application deadline.

GSST reserves the right to verify the authenticity of your educational diploma and transcripts:

  • Request additional information to verify an application.
  • Reject the application if it is proven, or if the University has reasonable belief, that the information provided is false or if the applicant refuses to provide the requested information, whether or not an offer has already been made. 
  • For further information on applying, assessment procedures, etc. please see the GSST application guide here.  

Please note:

  • The programme committee may request further information or invite the applicant to attend an interview.

All interested candidates are encouraged to apply, regardless of their personal background.