Paschen Notation Research Articles

Hanle effect measurement of neon 2p 5 3p level lifetimes

The lifetimes of eight of the neon 2p levels (Paschen notation) have been measured using the Hanle effect in a mild helium-neon discharge. Most of these levels show evidence of cascade of alignement from the 2s 4, 3s 1 and 3d levels when, at low pressures, these levels are partially aligned, as are the 2p levels. Data obtained at higher pressures are found to be free of cascade effects and are used to establish upper limits for the lifetimes of the 2p levels, the results being subject to coherence narrowing. A correction for the coherence narrowing is estimated resulting in the following natural lifetimes in ns: 2p 2 17.6(6); 2p 4 19.2(1.0); 2p 5 18.6(1.3); 2p 6 18.2(7); 2p 7 19.4(9); 2p 8 19.6(1.0); 2p 9 18.7(7); 2p 10 24.6(5). These values are systematically less than those obtained by methods in which cascade effects have not been carefully eliminated. In common with other Hanle effect measurements for these levels, they are also marginally smaller than the lifetimes given by Bennett and Kindlmann.

Cascade effects in neon life time measurements

Alignment cascade phenomena have been studied in the neon 2p levels (Paschen notation) Hanle effect and double resonance techniques in a mild discharge. The levels are aligned directly by an optical excitation mechanism. Most 2p levels show evidence of alignment cascade from the 2s4, 3s1 or 3d levels below 0.1 Torr; addition of argon impurities greatly enhances the cascade signal relative to the direct alignment signal. Data used previously in pressure broadening studies are shown to be free of cascade errors and are used to establish upper limits for the 2p level life times. A correction for coherence narrowing is estimated; this gives natural life times systematically less than those obtained by methods in which cascade effects are not carefully eliminated. In common with other Hanle effect measurements for these levels the values are marginally smaller than the threshold life times of Bennett and Kindlmann (1966).

Additional Excitation Transfer between Excited Helium Atoms and Neon in He–Ne Laser Discharges

Measurements are given of the ratio of the excitation due to helium to the excitation due to electrons for a number of neon states in a He–Ne laser discharge. The ratio was obtained from spectral intensity measurements on dc discharges in pure neon at a pD of 2.2 Torr mm and in a helium-neon 5:1 mixture at a pD of 4 Torr mm, with a discharge tube diameter of 10 mm, at a current density of 0.23 A cm−2, where the electron temperature is deliberately chosen to be the same in both discharges. In Paschen notation, the ratios are 4d5−6; 5d4, 5d4′, 4d3, 4d1″, 4d1′, 4s3−7; 5d4, 5d4′, 5d3, 5d1′−8; 4s5−9, 4s4−51; 4s2−29; 5s3−3.5; and 5s2−12. It is shown that a selective-excitation reaction involving He 21P1 atoms is responsible for the excitation of neon atoms to the Ne-5s2 state. The reaction is spin conserved and has a cross section of about 10−16 cm2.

Pressure broadening of the Hanle effect in a neon discharge

Investigates the levels of the 2p53p configuration of neon by studying the polarization of the light emitted by a dc neon discharge. The pressure broadening of the Hanle signals was studied and cross sections were obtained for the destruction of alignment for collisions with both helium and neon ground state atoms. The measurements have been made at 315 K and 85 K. The cross sections for the 2p2 and 2p6 levels (Paschen notation) change considerably with temperature, while the cross sections for other levels are almost independent of temperature.

Effect of Helium on Population Inversion in the Helium-Neon Laser

Measurements are given of the ratio of the excitation due to helium to the excitation due to electrons for the 3s and the 2s levels (Paschen notation) of neon. The ratio was obtained from spectral intensity measurements on dc discharges in pure neon and in helium-neon mixtures with the electron temperature the same in the two cases. The excitation ratios for the Ne 3s levels at a discharge current density of 130 mA cm−2 in a 5:1 He–Ne mixture are 3s2−72, 3s3−4, 3s4−7, and 3s5−7; and for the Ne 2s levels in a 10:1 He–Ne mixture, 2s2−11, 2s3−20, 2s4−5, and 2s5−10.

Transition Probabilities and Mean Lives of the3s2Laser Level in Neon I

The mean life of the $3{s}_{2}$ (Paschen notation) laser level in Ne I has been measured for a series of pressures in the range of 3-7 \ensuremath{\mu}m Hg using a method of delayed coincidence. The lifetime values, obtained by means of the $3{s}_{2}\ensuremath{\rightarrow}2{p}_{4}$ (6328 \AA{}) transition, show an increase in magnitude with increasing pressure. This pressure dependence was interpreted as being due to the imprisonment of the 600.04 \AA{} radiation emitted in the transition of the $3{s}_{2}$ level to the ground state. The Holstein theory of the imprisonment of resonance radiation was applied to the analysis of the lifetime-versus-pressure data to yield the following results: ${A}_{600}=2.45\ifmmode\pm\else\textpm\fi{}0.20\ifmmode\times\else\texttimes\fi{}{10}^{7}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, ${f}_{600}=0.0040\ifmmode\pm\else\textpm\fi{}0.0003$, $\ensuremath{\Sigma}{}^{\ensuremath{'}}A=(\ensuremath{\Sigma}A\ensuremath{-}{A}_{600})=1.61\ifmmode\pm\else\textpm\fi{}0.12\ifmmode\times\else\texttimes\fi{}{10}^{7}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, and lifetimes of 25 \ifmmode\pm\else\textpm\fi{} 2 and 62 \ifmmode\pm\else\textpm\fi{} 5 nsec for the low-pressure and high-pressure limits, respectively. The error limits were derived from the standard deviations in the measured lifetimes and the measured pressures. Experimental results of other workers along with theoretical values calculated under various assumptions are presented for comparison with the results of the present work.

Transition probabilities and mean lives of the 2s 2 laser level in neon I

Values of sums of transition probabilities and mean lives associated with the 2 s 2 (Paschen notation) laser level in Ne I have been determined under various theoretical assumptions and are presented in comparison with available experimental results. Also, using intermediate coupling and the Hartree-Fock-Slater approximation, the probability of the 2 s 2 → 2 p 6 1 S 0 (626·8Å) transition was calculated and found to be 8·8×10 7 sec -1 The theoretical values were found to be in agreement with an extrapolation to zero pressure of a series of linewidth measurements of the 11 520 Å laser transition but in disagreement with the lifetime of the 2 s 2 level as determined from a delayed-coincidence experiment.

A calculation of repulsive force constants of the Lennard-Jones potential for some excited states of noble gases

Collision diameters and repulsive force constants of the Lennard-Jones potential are calculated for interactions between noble gas atoms, one of which is in an excited state. The excited-state atoms considered are neon (3s2, 2p4, 1s2) and argon (2p2, 1s2) (Paschen notation); the ground-state atoms are helium, neon and argon. It is shown that repulsive interactions between two atoms, one of which is in an excited state, are operative at much larger internuclear separations than those known for interactions between two unexcited atoms; the corresponding collision cross section for ground-state noble gas atom collisions is not at all representative when one of the interacting atoms is in an excited state.

A new cascade laser transition in HeNemixture

Selective molecular absorption technique was used to obtain population inversion between the 3 p 2 and the 2s 2 neon levels (Paschen notation) with resulting induced emission at λ = 2.3956 μ.

Experimental Lifetimes of the 5p Levels in Argon i*

Mean lives of 7 of the 10 5p atomic levels in Ar i have been determined using electronic excitation and a method of delayed coincidence. The measured values, in nanoseconds, of the mean lives of the 3p1 and 3p5 through 3p10 levels (Paschen notation) in neutral argon are: 3p1, 71±2; 3p5, 95±2; 3p6, 124±3; 3p7, 149±3; 3p8, 166±5; 3p9, 141±2; and 3p10, 189±3. The error given with each lifetime is the standard deviation in the mean as evaluated from the dispersion of the individual measurements. Wavelengths used in the determinations ranged from 4159 to 4702 A. The lifetimes were estimated to contain systematic errors varying from 5% to 15% and are presented in comparison with values obtained by combining theoretical calculations with other experimental results.

Neon Transition Probabilities*

Relative transition probabilities for 12 visible neon lines originating on the 3s2 and 3s3 (Paschen notation) levels of neon have been measured. The experimental technique utilizes the interaction between the output of a helium–neon laser oscillating at 3.39 μ (3s2–3p4) and the excited atoms in a neon discharge. Changes of intensity of spontaneous emission from the 3s2 and 3s3 levels result from this interaction. By analyzing these intensity changes as a function of pressure, we have determined the ratio of the transition probabilities for the 3s2–3p4 and the 3s2–2p5 transitions. This ratio is 7.10±0.57. The measurements also yield the product of the radiative lifetime of the 3s3 level and the effective cross section for transfer of excitation between the 3s2 and 3s3 levels. This product is τ3σ23 = (9.93±0.80)×10−23 sec-cm2. The transition probabilities are placed on an absolute scale by use of a recently reported absolute value for the 3s2–2p4 transition. The experimental values are compared with the theoretically calculated transition probabilities for which a j-l coupling model was used. This comparison points out the rather large departure of these levels from j-l coupling.

Lifetimes of Some 4p Levels in Argon I*

Mean lives of four electronically excited atomic levels in Ar i have been determined using a method of delayed coincidence. The measured values of the mean lives of the 2p1 through 2p4 (Paschen notation) levels in neutral argon determined from transitions with associated wavelengths extending from 6677 to 7147 Å are as follows: 2p1, 21±2 nsec; 2p2, 25±1 nsec; 2p3, 26±1 nsec, and 2p4, 31±2 nsec. The lifetimes were estimated to contain systematic errors varying from 5% to 15% and are presented in comparison with results of other workers.

Self broadening and f -values in the spectrum of neon

Profiles of lines in the NeI spectrum arising from transitions between the configurations 2 p 5 3 s and 2 p 5 3 p were measured by means of a direct-recording Fabry–Perot interferometer. The d. c. discharge was cooled with liquid nitrogen or ice and currents were typically 0·5 mA. Full analysis of the profiles determines the pressure broadening as a Lorentzian component. For lines with the lower level 2 s 2 (Paschen notation) the broadening can be ascribed to the resonance interaction alone and the f -value of 0·16 8 is obtained for the resonance transition 736 Å. From coupling parameters the f -value of the transition 744 Å is estimated as 0·01 2 which is consistent with the broadening observed for the lines with the lower level 2 s 4 . The nature of the higher order interactions is discussed with reference to the observed temperature dependence and pressure shifts. Extrapolation of the Lorentzian width to zero density and the subtraction of a carefully determined instrumental contribution gives a value in excess of the radiation width for the level 2 s 2 , a result similar to that reported for the level 2 1 P 1 in helium. The explanation of this anomaly as an enhancement effect is discussed.

Atomic Lifetimes in Neon I

Mean lives of a number of electronically excited atomic levels in Ne i have been determined using a method of delayed coincidence. Following a detailed description of the experimental procedure and a discussion of a series of trial runs in He i, the measured values of the mean lives of the $2{p}_{1}$ through $2{p}_{9}$, $3{p}_{1}$, $3{p}_{10}$, and $4{{d}_{1}}^{\ensuremath{'}}$ (Paschen notation) levels in neutral neon are given. These lifetimes, determined from transitions with associated wavelengths extending from \ensuremath{\approx}3400 to \ensuremath{\approx}6400 \AA{}, ranged in value from \ensuremath{\approx} 14 to \ensuremath{\approx} 500 nsec. The lifetimes were estimated to contain possible systematic errors varying from 5 to 20% and are presented in comparison with corresponding results of other workers.

Atomic Lifetimes in Neon I.

Mean lives of a number of electronically excited atomic levels in Ne i have been determined using a method of delayed coincidence. Following a detailed description of the experimental procedure and a discussion of a series of trial runs in He i, the measured values of the mean lives of the $2{p}_{1}$ through $2{p}_{9}$, $3{p}_{1}$, $3{p}_{10}$, and $4{{d}_{1}}^{\ensuremath{'}}$ (Paschen notation) levels in neutral neon are given. These lifetimes, determined from transitions with associated wavelengths extending from \ensuremath{\approx}3400 to \ensuremath{\approx}6400 \AA{}, ranged in value from \ensuremath{\approx} 14 to \ensuremath{\approx} 500 nsec. The lifetimes were estimated to contain possible systematic errors varying from 5 to 20% and are presented in comparison with corresponding results of other workers.

Stark Broadening of Isolated Spectral Lines from Heavy Elements in a Plasma

The frequency distributions of neutral cesium and argon lines broadened by local fields of both electrons and ions in a plasma are calculated in the classical path approximation. The electron collisions are treated by an impact theory originally developed for neutral helium lines which takes into account deviations from adiabaticity. For the ion effects the adiabatic and in most instances also the quasi-static approximation can be used, if necessary corrected for ion-ion correlations and Debye shielding. Atomic matrix elements are obtained with the Bates and Damgaard method and are checked against measured Stark coefficients. Stark broadening parameters are tabulated for the argon lines arising from $2p$ and $3p$ levels (Paschen's notation) and for the cesium lines in the series $6S\ensuremath{-}nP$, $6P\ensuremath{-}nD$ with $n$ up to 20, $6P\ensuremath{-}nS$ with $n$ up to 15, and $5D\ensuremath{-}nF$ with $n$ up to 10. Approximate formulas for total widths and shifts are suggested. For the widths, an accuracy of 20% is indicated by the good agreement with experiments. Measured shifts are only available for argon. Here the calculated shifts tend to be 20% larger than the measured values.

Excitation of Forbidden Spectral Lines

HANSEN, Takamine, and Werner (Kgl. Danske Videnskab. Selskab Mathfys. Medd. 3) have observed the line 1S – 2p1 (Paschen's notation) of mercury in a condensed discharge, and Takamine and Fukuda (Phys. Rev. 25, p. 23, 1925) have found the line strongly developed in the glow of a branched arc. We have excited this line, the corresponding line of zinc, and both 1S – 2p1 and 1S – 2p3 of cadmium in the positive column of a hot-cathode discharge. The positive column was viewed end-on while the cathode glow was confined to a side tube. The potential difference across the entire tube was of the order of 100 volts, but the tubes employed were of such length, 30 to 100 cm., that the voltage drop per mean free path of an electron was quite small. The spectrum is strictly of the arc type, only a few of the more readily excited spark lines appearing, and these in comparatively low intensity.