hodges_1981 =========== R\. V\. Hodges, L\. C\. Lee and J\. T\. Moseley, "Multiphoton ionization of Xe and several small molecules at 193 and 248 nm", Int\. J\. Mass Spectrom\. Ion Phys\. 39, 133\-143 \(1981\) `Source record `__ · :doc:`Catalogue ` · :doc:`Review register ` DOI: `10\.1016/0020\-7381\(81\)80027\-7 `__ **Source kind:** measurement **Recorded technique:** Multiphoton ionisation in a drift\-tube mass spectrometer \(pp\. 134\-137\)\: a Lambda Physik EMG 500 excimer laser \(ArF 193 nm, KrF 248 nm\) focused by a 50 cm radius mirror to an oval of about 0\.5 x 1 cm2 in front of the exit aperture of a drift tube filled to 50\-200 mtorr \(most gases diluted in He\); the positive ions extracted by the drift field \(90 Td\) into a quadrupole mass spectrometer and counted in a multichannel analyser with a time\-of\-flight module triggered by the laser\. Laser power measured after the tube with a surface\-absorbing calorimeter and varied by the discharge voltage, the gas circulation speed or wire screens\. The power density at the aperture estimated from the beam area and average power measured at the aperture's position and 'the manufacturer's specified pulse duration \(10\-15 ns\)'\: '0\.8 and 3 MW cm^\-2' at 193 and 248 nm \(p\. 137\)\. Xe at 5, 10 and 20 mtorr \(193 nm, Table 2\) and 50 mtorr \(248 nm, Table 1\)\. **Materials in structured entries:** Xe **Dataset quantities:** multiphoton\_ionization\_cross\_section **Contents:** 1 dataset; 0 formulas. Curation notes -------------- Journal pp\. 133\-143 = PDF pages 1\-11 \(a scan with a text layer\)\. Identity checked on the first page \(International Journal of Mass Spectrometry and Ion Physics, 39 \(1981\) 133\-143; Ronald V\. Hodges, L\. C\. Lee and J\. T\. Moseley, SRI International; first received 25 September 1980, in final form 14 November 1980\) on 2026\-10\-09\. WHAT THE PAPER MEASURES\: relative multiphoton ionisation rates, 'the ratio between the average number of ions formed per pulse and the partial pressure of the ionized gas' \(p\. 138\), in ion counts/\(pulse mtorr\), with no correction for the mass dependence of the quadrupole's transmission; 'the uncertainty in the relative ionization rates within each Table is probably less than a factor of two' \(p\. 138\)\. Xe\: 0\.4 at 193 nm and 0\.8 MW/cm2 \(Table 2, p\. 137\), 0\.0004 at 248 nm and 3 MW/cm2 \(Table 1, p\. 136; three photons\)\. The power dependence of Xe at 193 nm \(Fig\. 2\) has a non\-integral slope, attributed to the spatial non\-uniformity of the beam \(p\. 135\)\. THE DEFINITION \(p\. 138, Eq\. 1\), quoted\: 'The two\-photon cross\-section, alpha, at 193 nm can be estimated from our data using the expression \[3\] n\+/n0 = alpha I^2 tau / h nu \(1\) where n\+ is the number of ions detected per pulse, n0 is the number of Xe atoms in the volume sampled by the exit aperture and intersected by the laser beam \(~0\.004 cm3\), I is the laser flux, and tau is the pulse duration\.' So the ionisation rate per atom is alpha I^2 / h nu, I in W cm^\-2\: the definition of mccown\_1982's Eq\. \(9\) and of bischel\_1979's W\_fg = alpha I^2 / hbar omega \(the paper's Ref\. 3\), with a square pulse\. The generalised cross section on the photon flux is sigma\_2 = alpha h nu \(h nu = 6\.42 eV at 193 nm\)\: 5\.1e\-52 cm4 s for alpha = 5e\-34 cm4 W\-1 \(not printed by the paper\)\. THE VALUE \(p\. 138\)\: 'At 193 nm, for a laser flux of 0\.8 MW cm^\-2, we obtain alpha = 5 x 10^\-34 cm4 W^\-1\. This value should be considered a lower limit, since eqn\. \(1\) does not include the mass\-spectrometer detection efficiency\.' CONSISTENCY\: Eq\. \(1\) with Table 2's 0\.4 ion counts/\(pulse mtorr\), the 0\.004 cm3 volume \(Xe at 296 K, the temperature not stated\: 1\.3e11 atoms per mtorr\), 0\.8 MW/cm2 and h nu = 6\.42 eV gives 4\.9e\-34 cm4 W\-1 for tau = 10 ns and 3\.3e\-34 for 15 ns \(the specified 10\-15 ns\)\: the printed 5e\-34 is the 10 ns end\. QUOTED ELSEWHERE, CHECKED\: mccown\_1982 \(TC\-884\) quotes 'the lower limit for alpha to be 5 x 10^\-34 cm4 W\-1' and holds it in Table I as Hodges, Lee and Moseley's\: the value and its being a lower limit match\. McCown et al\.'s 4e\-32 cm4 W\-1 is 80 times this lower limit\. The paper quotes Bischel et al\. \(Ref\. 3\)\: 'Bischel et al\. \[3\] have estimated a cross\-section of 1 x 10^\-34 cm4 W^\-1\. However, they point out that participation of autoionizing states could increase this value by a factor of ~10^2' \(p\. 138\)\: both match bischel\_1979 \(Table I and p\. 386\)\. NOT TAKEN\: the relative ionisation rates of Tables 1 and 2 \(ion counts per pulse and mtorr, not a quantity of the vocabulary, and uncorrected for the mass filter's transmission\), including Xe's three\-photon rate at 248 nm; Fig\. 2 \(the power dependence of Xe at 193 nm, relative\)\. Nothing else is in cm4 W\-1\. Further two\-photon data the paper cites, not in the library\: D\. Kligler, D\. Pritchard, W\. K\. Bischel and C\. K\. Rhodes, J\. Appl\. Phys\. 49, 2219 \(1978\) \(Xe two\-photon excitation at 248 nm, its Ref\. 9\)\. **Recorded bibliographic identity status:** VALIDATED\_WITH\_WARNINGS. This concerns identification of the source; it does not establish the scientific correctness of its contents. Datasets -------- hodges\_1981/alpha\_Xe ~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "alpha_Xe", "material": "Xe", "table": "text", "scale": 1e-34, "quantity": "multiphoton_ionization_cross_section", "unit": "cm4 W-1", "abscissa_unit": "nm", "use": "check", "uncertainty": { "level": "not stated" }, "parameters": { "photons": 2, "polarization": "not stated", "method": "ions per pulse counted by a quadrupole mass spectrometer behind a drift tube, Xe at 5-20 mtorr, ArF laser; Eq. (1) with an estimated sampled volume (0.004 cm3), power density and pulse duration; detection efficiency not included", "definition": "n+/n0 = alpha I^2 tau / h nu (Eq. 1, p. 138): n+ the ions detected per pulse, n0 the Xe atoms in the sampled volume (~0.004 cm3), I the laser flux (W cm^-2), tau the pulse duration; alpha in cm4 W^-1", "wavelength_nm": 193, "intensity_w_cm2": 800000.0, "intensity_definition": "'laser power fluxes of 0.8 ... MW cm^-2' at the exit aperture, from the measured beam area and average power and 'the manufacturer's specified pulse duration (10-15 ns)' (p. 137)", "pressure_range_mtorr": [ 5, 20 ], "limit": "lower" } } 1 inline points in the source record. p\. 138\: 'At 193 nm, for a laser flux of 0\.8 MW cm^\-2, we obtain alpha = 5 x 10^\-34 cm4 W^\-1\. This value should be considered a lower limit, since eqn\. \(1\) does not include the mass\-spectrometer detection efficiency\.' The source's own coefficient \(rate per atom alpha I^2 / h nu\), not the photon\-flux cross section \(sigma\_2 = alpha h nu = 5\.1e\-52 cm4 s\)\. A lower limit\: use = check\. Formulas -------- No formulas are recorded. Corrections ----------- No dataset errata are recorded in this source record. Formula corrections, where recorded, appear with their formulas above. Curation notes may also discuss corrections or unresolved interpretation. Consult the :doc:`review register ` for the checks and decisions.