Laura McKemmish

Laura McKemmish

Laura McKemmish

Lecturer

Contact details

Email: l.mckemmish@gmail.com

Office

Group Website at UNSW: http://www.chemistry.unsw.edu.au/mckemmish-group

Research Websitehttps://sites.google.com/view/laurakmckemmish/home

Biographical Details

I completed my Bachelor of Science (Advanced) at the University of Sydney in 2010 and was awarded a University Medal for my Honours research in Chemistry. My PhD was conferred for a thesis on "Mixed Ramp-Gaussian Basis Sets" in May 2015 from the Australian National University's Chemistry department. I was a post-doctoral researcher in the ExoMol group in University College London's Physics and Astronomy department from September 2014-June 2016, and a Marie Sklodowska-Curie fellow from July 2016-December 2017. I have been a Lecturer at UNSW Chemistry since January 2018.

My Research

I consider myself to be a quantum chemist and molecular physicist. My expertise is in theoretical and computational modelling of molecules, particularly their spectroscopy. I love interdisciplinary work and combining interesting methods with interesting applications.

Selected Honours Projects

Ultracold Alkali Metal Dimers

Molecules like Rb2 and LiCs may not seem like reasonable chemical species – they are usually bound more than 10-20 times more weakly than CO. But for ultracold molecular physicists, these alkali metal dimer species are their key weapon of choice in the search for unusual quantum behaviours, unusual chemistry, new physics and a better understanding of the universe. Turns out that these sorts of species can be formed at nano-Kelvin temperatures by using light to form bonds between laser cooled ultracold atomic species such as Li, Na, Rb and Cs. Their ultracold temperature means quantum mechanics is everything and their interactions can be controlled exquisitely to allow discovery of new unusual science. To facilitate these experiments, experimental designers must have access to detailed complete descriptions of their coupled rovibronic structure including their absorption properties. In this project, you will be producing this data for a set of molecules using diverse tools including high-level electronic structure calculations, a newly developed nuclear motion code and literature experimental spectroscopic data.
 

Intramolecular Energy Flow in Small Molecules after Excitation

Despite their size, at high temperatures, small molecules (with 2-5 atoms) often have thousands to millions of relevant rovibronic or rovibrational energy levels and millions to billions of relevant transitions. The question of what happens to a small hot molecule after excitation to a high level rovibronic or rovibrational energy level thus becomes quite complex. Many undergraduate, post-graduate and post-doctoral projects in the ExoMol group at University College London have been devoted to producing so-called “line-lists” containing data for all the relevant energy levels and transitions for small molecules including water, ammonia, methane, vanadium oxide and more. Part of this data is the intensity of transitions between various energy levels; this data is waiting to be explored in more depth to answer new questions about relaxation processes in isolated molecules.

In this project, we will be using the existing ExoMol line-list data to ask new questions and gain new understanding. Does relaxation from an excited state to the ground state generally only take a few steps, or hundreds? Is the rotational energy generally lost before vibrational energy, is it the reverse or is it a mix? How common is vibrational relaxation, internal conversion and intersystem crossing in an isolated molecule that doesn’t collide with other species? How does this depend on the molecule and on which particular energy level is excited? In this project, you will be given the data, shown how to ask questions of the data and left to explore, asking new questions and finding new answers.

Collaborative Projects: Incorporating some Theory into your Synthetic or Spectroscopy research Project

Selected Undergraduate Research Projects

These are appropriate as both summer and CHEM3998 projects.

Molecular Data for Astrophysics of Cool Stars and Hot Jupiter Exoplanets

The atmospheres of cool stars and hot Jupiters with temperatures of 1500-4000 K can be filled with unusual chemical species including the weird, complex and very colourful transition metal diatomic oxides, TiO, VO, ZrO, CeO, FeO and YO. Their importance in stellar and probably hot exoplanetary atmospheres means there is significant impetus to understand these spectra to very high precision; for example, detecting and characterising potential habitable exoplanetary atmospheres around red dwarfs will require high accuracy TiO spectroscopy data.

I have worked recently on developing high level models of the spectroscopy of hot TiO and VO. Though quite successful, this research is ultimately limited by the quality of computational chemistry.

Developing better, new computational chemistry methods is much easier with high quality experimental benchmark data is available. For almost 40 years, scientists have been using the 1979 Huber-Herzberg database of diatomic constants – this has not been updated. It is time to add the nearly 40 years of experiment to the compilation! This is a huge undertaking, so for this summer project we are going to focus on unusual transition metal diatomic oxides for which there is (1) an immediate application for the data and (2) good previous compilations of relevant experimental data.

This project requires basic quantum mechanics and spectroscopy. No prior astronomy or computational chemistry is required, though the student should be interested in the topics. With strong performance, the student on this project may be invited to be a co-author on an upcoming scientific paper.

UNSWChemistry FilmMakers

Short videos are a powerful medium to communicate scientific ideas in an engaging and informative manner, as illustrated by the success of the YouTube format. There is great Chemistry content on YouTube, but little about Chemistry research at universities.

In this short project, we are going to be bringing viewers into the UNSW School of Chemistry to learn about the cutting-edge science done by its researchers. You will be working with interested UNSW researchers from across the school to produce short videos on their research. You can expect to be learning about a variety of research areas, conducting interviews of expert researchers, filming experiments (safely!) and imagining creative “B-roll” to support the story-telling.

This project requires no previous filmmaking experience; enthusiasm, a willingness to learn, curiosity, computer skills and independence are the key qualities I am looking for. This is an excellent opportunity to learn more about potential research topics for a future Honours or PhD project.

Updating A Highly Cited Reference Database

The Huber-Herzberg database of diatomic molecular constants such as bond lengths, vibrational frequencies and dissociation energies was collated from 1969 to 1979 and has since been cited more than 15,000 times, with about one citation a day almost forty years after the original publication. Spectroscopists have been working extremely hard to produce additional data on a wide range of molecules, while theory has improved beyond recognition from the 1979-era calculations, yet this diatomic data has not been updated and is still being used.

This summer project is part of a much larger project (https://sites.google.com/view/orbyts/diatomic-constants) to update this via many people entering data using an online interface. You will be using existing online databases including the Computational Chemistry Database and the NIST Chemistry Webbook (which digitises the original Huber-Herzberg data) to populate our new DC (Diatomic Constants) database. This initial data can be used to check the reasonableness of data entered by students in the future; for example, if a student enters a vibrational frequency twice as large as the theoretical value, a warning message can be given and an experienced scientist can look at the data.

This project requires the student to have a solid understanding of Python, with familiarity with databases, HTML, SQL and Django desirable. This will be a primarily computational project with large data science components. With a high level of performance, the student may be invited to be a co-author on an upcoming scientific paper.

Selected Research Projects

Using Molecular Spectroscopy to find New Physics

At its heart, fundamental physics has a problem: general relativity describing heavy objects and quantum mechanics (generalised to the standard model of matter) describing small objects do not work together and we cannot describe heavy small objects like black holes. The Large Hadron Collider has not yet produced new physics. Therefore, alternate experiments are imperative. One such experiment involves measuring whether the proton-to-electron mass ratio has varied over time or over space. Note that though this is a fundamental constant in our current understanding, many theories beyond the standard model predict variations – this variation can be measured through a shift in the spectral frequency of some transition frequencies. Spectroscopic measurements are the most accurate measurement humans can currently make and thus ideal for this high accuracy measurement. Measurement accuracy can be optimised by careful selection of a molecule and transition. Theoretical support is vital in both finding this molecule and transition, and in connecting a change in the observed spectroscopic measurement to a variation in this mass ratio.

This project will involve establishing a comprehensive set of criteria for a good target transition for experiments investigating proton-to-electron mass ratio variation for both astronomy and laboratory experiments. These criteria will then be applied to analyse the suitability of transitions in a small number of molecular systems.

Construction of an ExoMol Line List

A line list contains a list of all the energy levels & transitions within a small molecule (with some criteria on maximum energy etc). ExoMol is a particular database containing line lists usually producing using similar variational methodologies with experimentally-refined potential energy curves. The ExoMol database and methodology was established by an ERC grant (2011-2016) at University College London led by Prof. Jonathan Tennyson and Dr Sergey Yurchenko; contributors to the ExoMol database are now working worldwide (e.g. Germany, Wales and now Australia).

I am very happy to supervise the construction of line lists for diatomic molecules.

Different diatomics have varying complexity in terms of electronic structure, available theoretical data, possible upgraded ab initio electronic structure theory (quantum chemistry) calculation methods & available experimental data.

All diatomic line lists constructed by members of my group will use Duo, a general rovibronic nuclear motion code for diatomic molecules that allows treatment of many coupled electronic states and fitting to experimental energy levels.

Some projects will use existing ab initio data while others will calculate new curves.

Almost all projects will build first on a set of experimental energy levels, often obtained using a MARVEL analysis of the assigned experimental transitions (see below)

MARVEL analysis: Obtaining Experimental Energy Levels from Assigned Experiment Transitions

Experimentalists measure transition frequencies, or differences between energy levels, but, as theoreticians and modellers, it is much more useful to work with energy levels when, for example, we compare against theory, refine potential energy curves and produce line lists.

Further, a set of transition frequencies can be internally inconsistent; i.e. there is no set of energy levels that reproduces all the transition frequencies correctly. This issue can be particularly serious if there is a large amount of data from varying sources, but occurs to some extent will all spectroscopic data as the experimental frequencies have non-zero uncertainties.

MARVEL is a software code developed by Tibor Furtenbacher, Attila G. Császár (Hungary) that takes as input assigned transitions with uncertainties and produces energy levels with uncertainties. The program works by building up spectroscopic networks (graphs) by which energy levels (nodes) are connected by transitions (lines); the quality of the energy level determination increases when more transitions are to or from that level. The internal process allows identification of transitions that don't fit into the overall spectroscopic network and recommends increased uncertainties. Using this output as guidance, the user identifies mis-assigned lines, typos and underestimated uncertainties as an iterative process to work toward a self-consistent set of input transition frequencies with output energy levels.

In practice, a MARVEL project proceeds as follows:

  1. Find all available spectroscopic data for the molecule via a thorough literature review
  2. Digitise available spectroscopic data
  3. Convert data to MARVEL format, including consistent quantum numbers
  4. Use MARVEL online interface to produce the self consistent list of input transitions and output energy levels

MARVEL projects vary considerably in scope depending on (1) the complexity of the molecule's quantum numbers/ assignments and (2) the quantity and quality of the available spectroscopic data. In some cases, MARVEL may be used as a useful tool to provide energy levels for a line list fit; in other cases, the MARVEL analysis is a significant body of work in itself and is highly publishable (for example, H2O, TiO, C2, NH3, CH4 etc).

Updating the Huber-Herzberg Database of Diatomic Constants

In 1979, after 10 years of work, Huber & Herzberg released a collation of all existing data on diatomic spectra, including results from about 943 molecules, though for around 300 this only included dissociation energies. And from 1979 - 2018, more than 15,000 scientists have been using their data; on average, the database is still cited about once a day.

And at the same time, a whole army of experimentalists have been producing updating the data, producing new data often on completely new molecules, with theorists working hard to understand the electronic complexity of many of these small but very unusual species (e.g. ArXe!). But this new data is not readily available and thus not cited once a day by scientists worldwide.

My goal is to change this, to get new data of provable usefulness into a modern format, an online queryable database. To achieve this goal, I need to work with a big team with varying expertises and levels of experience.

So far, this has included:

  • Systems Managers (trained as computational chemists)
  • ORBYTS tutors to lead groups of high school students to find molecular constants
  • High school students given a molecule and asked to make it their own, finding out everything that has been found out about their molecule (and, ideally, suggesting what needs to be done next!)

In the future, we need to

  • Further develop the online database system, including its website
  • Refine the course for delivery in ORBYTS programs
  • Import data from existing online databases, e.g. NIST Chemistry Webbook (which has digitisation of original Huber-Herzberg database) and Computational Chemistry database