The broadening of a two-photon resonance is studied experimentally at the 4 s 1 S 0 −6 s 3 S 1 transition in a zinc atom upon absorption of two waves with a small detuning from an intermediate state in collisions with CO 2 , CO, and NO molecules. The measured absolute values of broadening cross sections greatly exceed gas-kinetic cross sections and are (9.4±2.4, 6.5±1.6, and 3.9±1.0)×10 − 14 cm 2 for CO 2 , CO, and NO, respectively. Anomalously large rate constants and cross sections obtained in experiments are explained by the efficient resonance quenching of the excited states of zinc atoms in collisions with molecules accompanied by transfer of the energy of excited atoms to vibrational-rotational degrees of freedom of molecules.
We report the first study of molecular-perturber-induced broadening of forbidden ground-to-Rydberg-state transitions. The
N2- and CO-induced-broadening cross sections for the $3S\ensuremath{-}\mathrm{nS} (\mathrm{nD})$ transitions of sodium have been measured for values of
n, the principal quantum number of the upper state, ranging from 4 to 41. These measurements, performed using the trilevel echo technique, were accomplished at sodium and perturber densities of ${10}^{\ensuremath{-}6}$ and 1 torr, respectively. The broadening rates, observed in the present experiment, differ in some respects from those observed previously with noble-gas perturbers. These differences, which presumably arise because of the presence of accessible internal degrees of freedom in the
N2 and CO perturbers (and in the case of CO also because of its permanent electric-dipole moment), are most clearly displayed in $3S\ensuremath{-}\mathrm{nS}$ transitions. Previous work has shown that with noble-gas perturbers the $3S\ensuremath{-}\mathrm{nS}$ broadening cross sections display a dramatic increase at low values of
n; they then decline at intermediate values of
n, and at high
n they approach a limiting value. In the present experiment we find that the initial increase in $3S\ensuremath{-}\mathrm{nS}$ broadening cross sections with
n is relatively small and more gradual. For high
n, the broadening cross sections become approximately constant. As is the case with noble-gas perturbers, the broadening of $3S\ensuremath{-}\mathrm{nD}$ transitions is generally larger than the broadening of the corresponding $3S\ensuremath{-}\mathrm{nS}$ transitions. With CO as a perturber, an unexplained irreproducibility in the broadening cross sections of high-
n $3S\ensuremath{-}\mathrm{nD}$ transitions is observed. One explanation has to do with the CO-induced frequency shifts being unusually large and exceeding the spectral width of our excitation lasers.
The study of molecular inelastic collision processes at cold and ultracold temperatures is of considerable interest as schemes are currently being developed to efficiently cool and trap neutral polar molecules. In this work, quantum-mechanical scattering calculations are presented for the quenching of rotationally excited CO due to collisions with H, He and H 2 for collision energies between 10 −5 and 10 cm −1 . The calculations were performed using the close-coupling approach and the coupled-states approximation. Cross sections for the quenching of the j = 1–10, 20, 30 and 40 levels of CO are presented and mechanism and trends of energy transfer in these systems are discussed.
The transfer of excitation energy, induced in inelastic collisions between excited Hg atoms and ground state Zn atoms, was studied using methods of sensitized fluorescence. Hg atoms in a low density Hg–Zn mixture were excited with Hg 2537 Å resonance radiation to the 63P1 state, and interacted with the Zn atoms which became collisionally excited to the 43P1 state and then decayed emitting sensitized fluorescence. Measurements of relative intensities of Hg 2537 Å resonance fluorescence and Zn 3076 Å sensitized fluorescence yielded the cross section of 5.9 × 10−2 Å2 for Hg(63P1) → Zn(43P1) excitation transfer. The addition of small quantities of N2 to the Hg–Zn vapor mixture enhanced the efficiency of the transfer. The cross section for quenching of the Zn 43P1 state by collisions with N2 was found to be 0.19 Å2.
Excitation transfer between the
62P21 and
62P23 resonance states in cesium, induced by Cs-
N2 and Cs-
H2 collisions, was observed in the first experiment of its kind, in which techniques of sensitized fluorescence are used to investigate collisional mixing between resonance states of alkali atoms in mixtures with molecular gases. The cesium-vapor-gas system, in which the cesium vapor pressure was low enough to avoid radiation trapping, was irradiated with a single component of the resonance doublet. The fluorescent light, which contained both components of the doublet, was monitored at right angles to the direction of excitation. Measurements of relative intensities of the fluorescent components yielded the following cross sections for excitation transfer and for quenching of resonance radiation. For Cs-
N2 collisions: ${Q}_{12}(^{2}P_{\frac{1}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=3.6$
A˚2, ${Q}_{21}(^{2}P_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=16.2$
A˚2, ${Q}_{10}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{1}{2}})=55.2$
A˚2, ${Q}_{20}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=63.5$
A˚2. For Cs-
H2 collisions:
Q12=6.7 A˚2,
Q21=29.6 A˚2,
Q10=11.7 A˚2,
Q20=6.7 A˚2. The large sizes of the excitation-transfer cross sections, which are comparable to the corresponding Cs-Cs cross sections, are attributed to resonances with transitions in the molecules.
Collisions of excited 113Cd(5 3P1) atoms with various molecular gases (N2, H2, D2, CO, CO2, CH4, C2H6, C2H4, O2) have been investigated using atomic fluorescence spectroscopy. By selective excitation of a hyperfine structure level with a pulsed dye laser and studying the time dependence of the fluorescence signals as a function of the buffer gas density the cross sections for quenching, fine structure transfer, and hyperfine structure transfer could be obtained. For N2 molecules the collisions can be described by a decoupling model as has been shown previously for the noble gases as collision partners.
The cross sections for the excitation energy transfer induced by collisions with He, Ar and Na ground-state atoms have been measured. The sodium atoms in the 4D state have been produced by two-photon excitation using cw laser radiation at 578.89 nm. Within a model which takes into account collisional population and depopulation of the 4F level as well as radiative relaxation (direct or cascade) of the 3D, 4P, 4D and 4F states ending in the 3P level, the rate for the collisional transfer turns out to be related to the ratio of the steady-state populations created in 3D and 4D states. They have been determined by measuring the fluorescence intensities of the and transitions. The measurements yield the following cross section values for those processes investigated: , and , at .