Knowledge Bank

OH emission bands have been observed, a the N.P.L. (England), between $1.2\mu$ and $3.3\mu$ by using a Michelson interferometer + Fourier transform. The source was a cold, low pressure flame developed in the laboratory of Dr. Broida (N.B.S). The covered spectral region contains the OH fundamental sequence $\Delta v=1$ from 3 to $3.3\mu$ as well as the sequence $\Delta v=2$ from 1.2 to $2.7\mu$. From the interferograms, spectra have been computed to give resolving powers of $23cm-1,4cm-1$ and $1.5cm-1$. The spectra under low resolution shows that the sequence $\Delta v=1$ is about five times more intense than the one $\Delta v=2$. The $\Delta v=1$ sequence, reported by Charters and Polanyi, with a resolving power of about $2.5cm-1$ is now studied with a resolving power of $1.5cm-1$, showing transitions $4\to 3$. For the $\Delta v=2$ sequence, Charters and Polanyi give only a small portion of the spectrum with a very low resolving power. For this sequence, in the region between 1.2 to $1.8\mu$, our resolution is even a little better than the OH high resolution spectra observed by Mrs. Connes and H. P. Gush, when studying the night sky by the interferometric method. However these observations were limited to $1.8\mu$ that is to say to transitions $6\to 4$. Our experiments gave the possibility, for the first time, to obtain the OH spectrum between $1.8\mu$ to $2.7\mu$ on cold, low pressure flames, the highest resolving power obtained up to the present being $1.5cm-1$. This kind of flames gives a much purer OH emission that hot oxy-acetylene flames. Transitions up to $12\to 10$ have been identified.