Observation of electric quadrupole transitions in the fundamental band ofO2in the 1600-cm−1region

We have detected the electric quadrupole $S\left(5\right)\mathrm{}$ and $S\left(7\right)\mathrm{}$ transitions in the 1-0 band of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}_2^{}{}_{}{}^{}$ using a tunable diode laser and a 40-m path of ${\mathrm{O}}_2$ at pressures of 10 to 80 Torr. This is the first observation of quadrupole vibrational transitions in a molecule other than hydrogen. Each transition is observed to be a triple due to the spin splitting of the ${\mathrm{O}}_2$ rotational levels, and the measured separations of the lines, in the 0.02 to 0.04-${\mathrm{cm}}^{-1\mathrm{}}$ range, agree with values derived from microwave spectroscopy of ${\mathrm{O}}_2$. The total integrated intensity of the ${\mathrm{O}}_2$ 1-0 quadrupole band was determined to be (1.77 ± 0.63) × ${10}^{-5\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$/(m amagat). We were not able to detect magnetic-dipole transitions in the band, and thus determined a conservative upper limit of 0.86×${10}^{-5\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$/(m amagat) for the strength of a magnetic-dipole 1-0 band in ${\mathrm{O}}_2$.