An upper limit of ${10}^{\ensuremath{-}2}$ ${\mathrm{\AA{}}}^{2}$ is obtained for the quenching cross section of sodium resonance fluorescence when the excited sodium atoms are in collision with inert-gas atoms in their ground state. Excitation of sodium vapor at a pressure of 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ Torr is followed by observation of the decay of the fluorescence using the method of delayed coincidences. The decay time of the fluorescence is unaffected by the presence of the inert gases He, Ne, A, Kr, and Xe at pressures up to 800 Torr, and at temperatures of 130 and 210\ifmmode^\circ\else\textdegree\fi{}C.
An upper limit of 10\ensuremath−2A˚2 is obtained for the quenching cross section of sodium resonance fluorescence when the excited sodium atoms are in collision with inert-gas atoms in their ground state. Excitation of sodium vapor at a pressure of 5\ifmmode\times\else\texttimes\fi{}10\ensuremath−7 Torr is followed by observation of the decay of the fluorescence using the method of delayed coincidences. The decay time of the fluorescence is unaffected by the presence of the inert gases He, Ne, A, Kr, and Xe at pressures up to 800 Torr, and at temperatures of 130 and 210\ifmmode^\circ\else\textdegree\fi{}C.
The total cross sections for inelastic collisions between sodium and inert gas atoms, leading to 3 2P1/2 ↔ 3 2P3/2 excitation transfer in sodium, have been determined in a series of sensitized fluorescence experiments with sodium – inert gas mixtures. The sodium vapor was maintained at a pressure of 5 × 10−7 mm Hg, at which there is no trapping of the resonance radiation, and the inert gas pressures ranged from 0 to 1 mm Hg. The cross sections Q1(3 2P1/2 → 3 2P3/2) and Q2(3 2P1/2 ← 3 2P3/2) are as follows: Na–He, 86.0 and 44.8 Å2; Na–Ne, 67.0 and 35.4 Å2; Na–Ar, 110 and 55.9 Å2; Na–Kr, 85.0 and 43.6 Å2; Na–Xe, 89.8 and 45.6 Å2. The ratios Q1/Q2 are in agreement with the value predicted from the principle of detailed balancing and the cross sections also agree, as to order of magnitude, with some theoretically predicted values.
The cross sections for quenching collisions between excited sodium atoms and N2, H2, HD, and D2 molecules in their electronic ground states have been determined using a delayed-coincidence method. The sodium atoms in mixtures with the gases were excited with 20-nsec pulses of NaD radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-pulse-height converter. The resulting pulse-height spectra, which were accummulated in a 400-channel kicksorter, yielded the effective lifetimes ${\ensuremath{\tau}}^{\ensuremath{'}}$ of the sodium resonance state, which are shorter than the natural lifetime $\ensuremath{\tau}$ because of the nonradiative decay induced in collisions with the molecules. The cross sections for collisions with N2, H2, HD, and D2, obtained from an analysis of the dependence of ${\ensuremath{\tau}}^{\ensuremath{'}}$ on the gas pressures, are 30.4\ifmmode\pm\else\textpm\fi{}1.2, 16.2\ifmmode\pm\else\textpm\fi{}0.3, 11.6\ifmmode\pm\else\textpm\fi{}0.4, and 9.8\ifmmode\pm\else\textpm\fi{}0.3 A˚2, respectively.
The met h o d of delayed coincidences for measu r i n g lifetimes of excited states has been used to investigate imprisonment of radiation in potassium vapor and to measure quenching cross sections in mixtures of potassium w ith diatomic gases and sodium wi t h noble gases.The me thod has also been u s e d to investigate the possibility that a longlived molec u l a r complex might be formed in inelastic collisions between 2 potassium and xenon, which lead to excitation transfer between the P potassium states.The alkali metal atoms were excited w i t h short pulses of resonance radiation, and the delays between the exciting and fluores cent pulses were m e a s u r e d w i t h a time-to-amplitude converter.At 10 3 pure potassium densities below 10 atoms/cm , the m e a s u r e d lifetimes approach the constant values of 27.8 + 0 .8 and 27.6 + 0 .8 nsec, 2 2 corresponding to the m e a n lifetimes of the 4 ^^2 anc* ^ ^3 / 2 s t a t e s > respectively.At higher densities, the apparent lifetimes are in satisfactory agreement w i t h the predictions of H o l s t e i n 's theory.The decrease in the apparent lifetimes, u p o n addition of diatomic gases to the potassium vapor, yielded cross sections for quenching collisions w it h N^, H^, HD and D^, which equal 34.0 + 2 .0 X2, 9.4 + 1.3 X2, 11.9 + 1.5 X2 and 8 .0 + 2 .0 X2, respectively.Addition of the noble gases He, Ne, Kr, Ar and Xe to sodium vapor did not lead to any measurable change in the decay rates for the sodium states within the iii
The cross sections for the collision-induced transfer of excitation from the 2P23 level to the 2P21 level of the first excited states of the alkali atoms have been measured for several alkali-noble gas systems. The cross sections were determined with a conventional resonance fluorescence technique in which the radiation from a spectral source was absorbed and re-emitted by an alkali vapor at low pressure (\ensuremath{\sim}${10}^{\ensuremath{-}6}$ Torr), and the scattered light analyzed with a scanning spectrometer. Provision was made for the introduction of various noble gases at controlled pressures into the alkali vapor. The determined cross sections are (in units of ${10}^{\ensuremath{-}16}$ cm2): Na-He, 41.1\ifmmode\pm\else\textpm\fi{}2.9; Na-Ne, 36.1\ifmmode\pm\else\textpm\fi{}2.5; Na-Ar, 64.6\ifmmode\pm\else\textpm\fi{}5.2; Na-Kr, 68.2\ifmmode\pm\else\textpm\fi{}5.5; Na-Xe, 61.8\ifmmode\pm\else\textpm\fi{}4.9; K-He, 52.8\ifmmode\pm\else\textpm\fi{}5.8; K-Ne, 14.0\ifmmode\pm\else\textpm\fi{}1.2; K-Ar, 34.0\ifmmode\pm\else\textpm\fi{}3.1. The quoted errors are estimated 70% confidence intervals. The measurements are compared with other experimental results and with various estimated cross sections.
The behavior of the sensitized fluorescent spectrum of sodium, produced by irradiating Hg–Na–N2 mixtures with Hg 2537 Å resonance radiation, was studied in relation to N2 pressure. In this ternary vapor-gas system, the sodium atoms become excited by collisional transfer from Hg 63P1 atoms and also from Hg 63P0 atoms which are formed in Hg(63P1) + N2 collisions. The spontaneous decay of the collisionally populated S, P, and D sodium states gives rise to the fluorescent spectrum and their radiationless decay (quenching) caused by collisions with N2 molecules, manifests itself in a decrease of the fluorescent intensities as N2 pressure is increased. An analysis of the variation of the fluorescent intensities with N2 pressure, yielded 15 quenching cross sections for various S, P, and D sodium states, which appear to exhibit resonance properties with respect to upward vibrational transitions in N2.
The effect of foreign gases upon the fluorescence of sodium vapor excited by the second line of the principal series has been investigated. The gases used were helium, nitrogen, and hydrogen and the intensities of both the 3303A line and the D light were observed. From the variation in intensity of the 3303A line as gas is added it is concluded that the presence of an inert gas has no appreciable effect upon the relative transition probabilities in the 32P state of sodium. With nitrogen or hydrogen as the added gas the D light intensity variation followed that of the 3303A line very closely but with helium a marked increase in intensity was produced by the first gas added with a decrease at higher pressures. This increase was explained as due to a transfer of sodium atoms from the 32P to the 32D state by collisions, thus increasing the number of atoms which radiate the D light. In addition to this increase in number the collisional transfers produced an increased "Doppler width" in the D light which persisted up to pressures well over 100 mm of helium and caused a decreased absorption of the fluorescence light. The bearing of this work on the difference in the intensity ratio of the ${2}^{2}S\ensuremath{-}{3}^{2}P$ and ${1}^{2}S\ensuremath{-}{3}^{2}P$ transitions as reported by Weiss for an arc and by Christensen and Rollefson in fluorescence is discussed. It is concluded on the basis of experimental evidence that any explanation of the difference which depends upon multiplicity of the 32P state is incorrect. An explanation of this difference based upon the assumption that the life period of an excited atom varies inversely as the transition probability of the radiation emitted is presented. It is shown that recent work on the life periods of atoms in the 23S1 state of mercury at least partially supports this assumption. A new type of sodium arc with increased intensity and stability of operation is described.