A technique is described in which flow velocities are measured by monitoring the ions produced in a laser-excited metal-vapor stream. The technique uses low-power lasers and low metal densities (∼10−3 Torr). It is used here to measure a flow velocity to an estimated uncertainty of 3%.

The quenching cross section of Bacl (C2Π) by He, An, and N2 have been measured by time-resolved laser-induced fluorescence decay method.(AIP)

We report the observation of doubly excited autoionizing Rydberg states of Sr, belonging to the configuration $5{p}_{\frac{1}{2}}$, $\mathrm{nl}$. Our procedure involves a three-step optical excitation process which incorporates Stark switching to reach higher $l$ states not normally accessible because of dipole selection rules. Quantum defects are reported for several $5{p}_{\frac{1}{2}}$, $\mathrm{ns}$ and $5{p}_{\frac{1}{2}}$, $\mathrm{nd}$ states. The lifetimes of the $5{p}_{\frac{1}{2}}$, $\mathrm{ns}$ states are shown to scale as ${({n}^{*})}^{3}$, and the lifetimes of the $5{p}_{\frac{1}{2}}$, $16l$ states are shown to increase dramatically with increasing $l$.

The cross sections for deactivation of the Na $5s\ensuremath{-}9s$ and $n=5\ensuremath{-}8$ manifold ($l\ensuremath{\ge}2$) states by ${\mathrm{N}}_{2}$ have been measured using a laser-induced fluorescence approach. The cross sections are: $6s$, 84(8) ${\mathrm{\AA{}}}^{2}$; $7s$, 82(9) ${\mathrm{\AA{}}}^{2}$; $8s$, 91(8) ${\mathrm{\AA{}}}^{2}$; $9s$, 104(10) ${\mathrm{\AA{}}}^{2}$; five manifold, 43(7) ${\mathrm{\AA{}}}^{2}$; six manifold, 36(8) ${\mathrm{\AA{}}}^{2}$; seven manifold, 32(7) ${\mathrm{\AA{}}}^{2}$; and eight manifold, 18(6) ${\mathrm{\AA{}}}^{2}$. The $s$-state cross sections are in qualitative agreement with a curve-crossing model. The decrease of the manifold cross sections with $n$ is attributed to the increasing multiplicity of the manifold with $n$.

The collisional deactivation of the Na $5s$ and $4p$ states by collisions with ${\mathrm{N}}_{2}$ molecules has been studied using the method of laser-induced fluorescence. The total cross sections for the depopulation of the $5s$ and $4p$ states are 86(8) and 43(4) ${\mathrm{\AA{}}}^{2}$, respectively. The cross sections for the specific collisional transfers $5s\ensuremath{\rightarrow}4p$, $5s\ensuremath{\rightarrow}3d$, and $4p\ensuremath{\rightarrow}3d$ are 32(8), 10(2), and 19(3) ${\mathrm{\AA{}}}^{2}$, respectively.

In Na, the energy gap $\ensuremath{\Delta}E$ between the $n$, $d$ state and the $n$, $l>2$ states is ten times larger than $\ensuremath{\Delta}E$ between $n$, $f$ and the $n$, $l>3$ states. To investigate the effect of this difference on the $d$- and $f$-state $l$-mixing cross sections, ${\ensuremath{\sigma}}_{d}$ and ${\ensuremath{\sigma}}_{f}$, we have recently carried out experiments to measure ${\ensuremath{\sigma}}_{d\ensuremath{-}f}$, the $l$-mixing cross sections for a microwave-induced mixture of $d$ and $f$ states. Using the previously measured values of ${\ensuremath{\sigma}}_{d}$, we have derived values of ${\ensuremath{\sigma}}_{f}$ which have the same $n$ dependence as ${\ensuremath{\sigma}}_{d}$. ${\ensuremath{\sigma}}_{f}$ is larger than ${\ensuremath{\sigma}}_{d}$ for Ne, but smaller for He and Ar. In addition, we have analyzed the final states after one collision with Ar using selective field ionization of the $17l$ states and have observed that after one collision all the $l$ states are equally populated indicating that there are no $\ensuremath{\Delta}l$ selection rules for the process. This confirms the earlier suggestion that $l$ mixing is caused by a short-range interaction.

We have observed the selective ionization of the degenerate $|{m}_{j}|$ levels of $s$, $p$, and $d$ states of sodium in the range of $n$ from 15 to 20 and have shown that atoms produced in these low-field (\ensuremath{\sim} 10 V/cm) states pass adiabatically from low-field $|{m}_{j}|$ to intermediate-field $|{m}_{l}|$ states. Experiments on the Stark manifold states in intermediate fields (\ensuremath{\sim} 1 kV/cm) and high fields (\ensuremath{\sim} 4 kV/cm) show that the $|{m}_{l}|=0 \mathrm{and} 1$ states pass adiabatically from intermediate- to high-field states and that the passage of the $|{m}_{l}|=2$ states is very nearly adiabatic. These findings suggest a general approach for predicting the threshold fields for ionization of atomic Rydberg states.

Using a laser-excitation, optical-detection scheme, we have observed microwave transitions from the $\mathrm{nd}$ to the $\mathrm{nf}$ and $\mathrm{ng}$ orbital levels in lithium states with principal quantum number $n$ from 7 to 11. These measurements yield precise values for the $d$, $f$, and $g$ state fine-structure intervals as well as $d\ensuremath{-}f$ and $d\ensuremath{-}g$ energy separations. Within the accuracy of these measurements, the fine structures are found to be hydrogenic. The dipole polarizability of the ${\mathrm{Li}}^{+}$ core is determined from the $d\ensuremath{-}f$ and $d\ensuremath{-}g$ energy splittings. The $d\ensuremath{-}f$ intervals are compared to pseudopotential calculations.

We report the measurement of $\mathrm{nd}\ensuremath{\rightarrow}(n+1)p$ intervals in sodium Rydberg states with $n=30\ensuremath{-}32$. The measurements were made using a microwave-resonance technique which utilizes selective field ionization. Fine-structure intervals of the $p$ state are reported and shown to continue the ${({n}^{*})}^{\ensuremath{-}3}$ scaling law, where ${n}^{*}=n\ensuremath{-}\ensuremath{\delta}$ is the effective quantum number and $\ensuremath{\delta}$ is the quantum defect. Quantum defects for the $p$ states are derived and compared to spectroscopic measurements.

The cross section for the process BaCl(C2Π32, ν = 0) + Ar → BaCl(C2Π12, ν = 0, 1, 2) + Ar was measured by a laser induced fluorescence technique and found to be 16(7) Å2. This cross section is much larger than the intermultiplet energy transfer cross sections in the alkalis based on a comparison of the fine structure splitting. It is concluded that in the molecular case coupling of internal degrees of freedom plays an important role.

Cross sections for the collisional l mixing of Na(n/sup 2/D) states from n = 5 to 14 by N/sub 2/ and CO have been measured by time-resolved laser fluorescence and calculated in a two-state approximation by assuming the perturbing gases are spherically symmetric. For both CO and N/sub 2/ the experimental cross sections rise sharply from n = 5 to n = 10 and remain constant for n > 10. The theoretical calculations overestimate the experimental cross sections by a factor of 3 from n = 10 to 12, but are in good agreement for the smaller n values.

The fine-structure intervals of the Na $11f$, $13f$, and $14f$ states have been measured by a microwave-resonance method yielding values of 10.52(21), 6.34(12), and 5.02(8) MHz, respectively. These values are \ensuremath{\sim}5% lower than the theoretical values for the corresponding hydrogenic states. We have also investigated the use of Ramsey's method of separated oscillatory fields as a means of obtaining narrower resonances.

A study of the spatially resolved chemiluminescence of the Ba + O2 reaction suggests that the emission is due to production of the excited states of BaO, Ba2O, and BaO2 formed in three-body recombination reactions.

Broad-band fluorescence at 4000 Å has been observed from gas phase mixtures of the dyes POPOP and α-NPO in Xe and Ar. The photon yields have been measured at 3 atm total pressure and are found to reach the following maximum values: α-NPO/Xe: 2%, α-NPO/Ar: 5%, POPOP/Xe: 9%, POPOP/Ar: 20%.

In the electric field ionization of highly excited $s$, $p$, and $d$ states of Na, we have observed one, two, and three ionization thresholds, respectively, reflecting the number of high-field $|{m}_{l}|$ states coming from the $s$, $p$, and $d$ states. Our observations indicate that the passage from low to intermediate field is adiabatic, and as a consequence we are able to achieve selective ionization of essentially degenerate low-field $|{m}_{l}|$ fine-structure levels.