Self-broadenings and frequency shifts of n 2 S and n 2 D Rydberg levels (up to n ~ 70) have been measured for rubidium in the pressure range of 3 to 100 mTorr, and the general dependence on principal quantum number n has been established for this low-pressure regime. A closer examination has revealed large (almost evenly spaced) oscillations in the dependence of linewidth on principal quantum number for the 2 S levels in the region of largest linewidth (n ~ 20 to 30) .The method of Doppler-free, two-photon spectroscopy, with instrumental linewidths of a few megahartz, is ideally suited to the study of small perturbations of atomic and molecular energy levels by collisions. This was demonstrated by Biraben etal. 1 in investigations of the shift and broadening of the 5 2 S and 4 2 D levels of sodium in collisions with noble gases, by Bolton, Harvey, and Stoicheff 2 for broadening of the ll 2 Dto 20 2 D levels of rubidium by argon, and recently by Weber and Niemax 3 for self-broadening of cesium levels up to 40 2 D. In this Letter, we report the results of 2 S-and 2 D -level shifts and broadenings in rubidium at pressures of 3 to 100 mTorr, for levels n = 10 to n~ 70. The present results constitute the most comprehensive study of line shift and line broadening for an atomic system to very high (n~70) Rydberg levels. Moreover, we report the first observation of pronounced oscillations in the dependence of linewidth on principal quantum number.The experimental method is based on Dopplerfree, two-photon spectroscopy with counterpropagating beams, 4 ' 5 and the use of an electrostatically shielded thermionic detector of high sensitivity. 6 A Kr + laser was used to pump a dye laser (Coherent Radiation CR599-21) producing a cw output of ~ 50 mW with a frequency jitter and linewidth of ~ 2 MHz in the wavelength region 593 to 656 nm. The dye-laser beam was chopped at 30 Hz; a small part was directed to a concave Fabry-Perot interferometer having a spectral-free range of 62.5 MHz; and the main portion was transmitted through an optical isolator (a Faraday rotator), then focused into a Rb cell, recollimated and focused into a second Rb cell, and finally, reflected back on itself with a concave mirror. Each Rb cell contained a thermionic detector. The resulting signals were amplified by lock-in amplifiers synchronized to the 30-Hz chopping frequency, and displayed along with the Fabry-Perot fringes on a three-pen chart recorder. Initially, the cells were baked and evacuated to ~ 1 X10" 8 Torr, before being charged with "lg of high-purity Rb in natural isotopic abundance (72% 85 Rb and 28% 87 Rb). Further purification was attempted in order to reduce the possible presence of Cs (occurring as an impurity at <500 ppm) by heating the cell and sidearm to ~ 220 °C for 12 h while condensing any vapors in an auxiliary cold trap. Each cell was placed in its own two-chamber oven with separate controls for the body and sidearm temperatures. In the reference cell, the sidearm was kept at 145 °C, corresponding to a Rb pressure of ~ 3 mTorr...

Doppler-free, two-photon spectroscopy has been used to investigate the transitions n2S ← 52S and n2D ← 52S of atomic rubidium, from n = 9 to 116 and n = 7 to 124, respectively, only 7.3 cm−1 from the ionization limit. Wavelengths of these transitions have been measured to an accuracy of 1 part in 107, and series formulae computed for term values and quantum defects. Hyperfine structure splittings in the 92S to 132S levels have also been measured.

Vibration–rotation spectra of HNO (DNO) have been observed in a flow system following the reaction of hydrogen (deuterium) atoms with NO. The spectra were recorded at approximately Doppler limited resolution with a large Fourier transform spectrometer. Complete analyses have been made of the ν1 bands of HNO and DNO with the following results (in cm−1).[Formula: see text]Spectra of ν2 (NO stretching) were also observed in both HNO and DNO, but ν3 (bending) proved too weak to be detected in either molecule.

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