Energy Transfer
The question of the exchange of energy on
collision is fundamental to the studies of reaction kinetics in gaseous systems
that were being pursued at the time of the opening of the PCL. The first direct
experiments had been made by James Lambert who learnt the technique from
Professor Arnold Eucken at Göttingen, where he spent the year 1936/37 as a
University Senior Student. On his return to Oxford, he became successor to
Hinshelwood (now Professor) as tutor at Trinity, and built an ultrasonic
apparatus in the Old Chemistry Department which had the necessary workshop
facilities under Fred March.
The interpretation of ultrasonic
measurements required accurate knowledge of second virial coefficients, which
were not usually available, and a Boyle's Law apparatus was constructed. Papers
on both topics for the case of acetaldehyde were published by Lambert and
Alexander in 1941 and 1942 (but were later shown to be erroneous). James
Lambert then joined the army as a Technical Staff Officer (Chemical Warfare).
He returned to the PCL in 1945, and the apparatus was transferred there.
His first Part II student was John
Rowlinson, who stayed on for a D.Phil. and switched his main concern to the
interesting thermodynamic implications arising from virial coefficient
measurements on different gases and mixtures at varying temperatures. Work in the
group continued on both aspects, and was extended to measurement of transport
properties. Ultrasonic measurements of vibrational and rotational relaxation
continued to be the main topic, and culminated in 1973 with the introduction of
a laser fluorescence technique for investigating the vibrational relaxation of
CO2(ν2) by O atoms.
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John Rowlinson – at
that time a D.Phil student with James Lambert – at work with the acoustic
interferometer. |
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James Lambert occupied his final years
before retirement writing the book Vibrational and Rotational Relaxation in
Gases (OUP, 1977), which appeared as No 1 of an International Series of
Monographs on Chemistry, edited appropriately by J.S. Rowlinson. This appeared
some ten years after any major review of the subject, and remains an
authoritative source of information.
Later, when Stephen Simpson came to the PCL
in 1969, he brought with him from the NPL his shock tube, and he has used that
to study gas phase vibrational energy transfer in the range 400 to 3000 K. He
has also used ultrasonic dispersion and photoacoustic methods near room
temperature and laser fluorescence from 350 to 60 K. Successful calculations
are at the level of the deactivation of 12C16O and 13C18O by 4He and by 3He: more complex cases demand a knowledge - not yet available of the
potential energy surfaces. It is even more difficult to understand VV transfer
in solution, but computer simulations on near resonant VV energy transfer by
Paul Madden and Glenn Evans (a regular visitor from the University of Oregon)
are beginning to point the way.
