Cavity ring down spectroscopy on the oxygen A band
in magnetic fields up to 20 Tesla
Abstract
Rotationally resolved spectra of the b\Sigma (v=0)<-- X\Sigma
(v=0) band of molecular oxygen are recorded by
cavity ring down (CRD)
spectroscopy in magnetic fields up to 20 Tesla. Measurements are
performed in a 3 cm long cavity, placed in the homogeneous field region
inside a Bitter magnet. CRD absorption spectra are measured with
linearly and circularly polarized light, leading to different \Delta M
selection rules in the molecular transition, thereby aiding in the
assignment of the spectra. Dispersion spectra are obtained by recording
the rate of polarization rotation, caused by magnetic circular
birefringence, using the Polarization Dependent CRD detection scheme.
Matrix elements for the Hamiltonian and for the transition moment are
presented on a Hund's case (a) basis in order to calculate the
frequencies and intensities of the rotational transitions of the oxygen
A band in a magnetic field. All spectral features can be reproduced,
even in the highest magnetic fields. The molar magnetic susceptibility
of oxygen is calculated as function of the magnetic field strength and
the temperature, and a discussion on the alignment of the oxygen
molecules in the magnetic field is given.
CRD spectrum of the central part of the A band
of molecular oxygen as
function of the magnetic field (in Tesla). Right-hand circularly
polarized light has been used to excite the molecules.
The vertical scale is the same for each spectrum, and has been omitted
for clarity. The spectrum measured in the
absence of a magnetic field is recorded under different experimental
conditions, in order to show the correct line intensities.
The transitions from the N=1, J=1, M=+1 level (around 13125 cm-1)
and the N=3, J=2, M=+1 level of the X\Sigma (v=0) state
towards the N'=J'=2, M'=+2 level of the b\Sigma (v=0) state are
indicated by the dashed lines.
(expand figure)
CRD spectrum of the central part of the A band
of molecular oxygen as
function of the magnetic field (in Tesla). Left-hand circularly
polarized light has been used to excite the molecules.
The vertical scale is the same for each spectrum, and has been omitted
for clarity. The spectrum measured in the
absence of a magnetic field is recorded under different experimental
conditions, in order to show the correct line intensities.
The transitions from the N=1, J=1, M=+1 level (around 13125 cm-1)
and the N=3, J=2, M=+1 level of the X\Sigma (v=0) state
towards the N'=J'=2, M'=0 level of the b\Sigma (v=0) state are
indicated by the dashed lines.
(expand figure)
