Edward O. Stejskal was a physical chemistry researcher known for nuclear magnetic resonance methods. His Illinois doctoral work used nuclear spin relaxation to investigate molecular motion in solids. At Wisconsin he developed pulsed field gradient NMR with his first doctoral student, John E. Tanner; later he worked at Monsanto and became a professor at North Carolina State University.^[ref]

Their 1965 apparatus measured proton spin echoes at $20.00\mathrm{MHz}$ using opposed gradient coils. Keeping the applied magnetic field gradient small during the radio frequency pulses and echo detection removed two limitations of continuously strong gradients: difficult excitation across a broad resonance and an echo too narrow to measure easily. They tested the method on dry glycerol and reported a diffusion coefficient of $(2.5\pm 0.2)\times 10^{-8}\mathrm{c}{\mathrm{m}}^2{\mathrm{s}}^{-1}$ at $26\pm 1{}^{\circ }\mathrm{C}$. This is their reported measurement, rather than a general reference value for all glycerol samples.^[ref]

The Stejskal-Tanner equation gives a useful ideal prediction. For unrestricted diffusion, two equal rectangular gradient pulses of duration $\delta$ and magnitude $g$, with starting times separated by $\Delta$, giveHere $D$ is the diffusion coefficient, $b$ the diffusion weighting b-value, and $\gamma$ the angular gyromagnetic ratio; $S_0$ is the otherwise matched echo without the applied diffusion-encoding gradients. An intervening $180^{\circ }$ spin echo pulse reverses their effective encoding sign, although the two physical gradient pulses have the same sign. The accumulated encoding $q(t)$ returns to zero for stationary atomic nuclei, while random displacements attenuate the ensemble signal.^[ref]

The finite-duration correction can be checked directly. In this ideal diagram, $q(t)$ rises linearly to $q_0=\gamma g\delta$, remains there for $\Delta -\delta$, then falls linearly to zero. Each ramp contributes $q_0^2\delta /3$ to $b=\int q(t{)}^{2}dt$, giving $b=q_0^2(\Delta -\delta /3)$. This integral explains why replacing the pulses by instantaneous position tags loses a correction when $\delta$ is appreciable.

At Monsanto, Stejskal and Jacob Schaefer combined cross-polarization (nuclear magnetic resonance) with magic angle spinning to obtain high-resolution solid-state nuclear magnetic resonance. In cross-polarization magic-angle spinning, polarization transfer strengthens weak nuclear responses while sample rotation averages appropriate anisotropic interactions; the two operations address different experimental obstacles.^[ref]

John E. Tanner was a physical chemistry researcher whose work with Edward O. Stejskal established pulsed field gradient NMR as a method for measuring self-diffusion. He studied physical chemistry at Oberlin, Indiana and Wisconsin, and later worked at Idaho National Laboratory. His early NMR work received renewed recognition with an honorary fellowship in 2016.^[ref]

The appeal of pulsed field gradient NMR was practical as well as theoretical: strong magnetic field gradients could encode motion without remaining strong during excitation or detection. In a 2017 interview with Derek Jones, Tanner recalled choosing Stejskal's laboratory because it had a magnet and because he wanted to measure slow diffusion. He also described rebuilding the probe to deal with eddy currents generated by switching the magnetic field gradients.^[ref]

Tanner made restricted diffusion experimentally concrete. He described assembling 99 layers of mica with aluminium foil spacers, carefully removing wrinkles and burrs to obtain regular gaps. Such a controlled geometry lets an echo probe displacement between known barriers, rather than treating every loss of NMR signal as free diffusion with a smaller diffusion coefficient.^[ref]

His 1970 work used a stimulated echo to extend the observation interval when spin-lattice relaxation is slower than transverse relaxation. The interval can store the relevant pattern as longitudinal magnetization, rather than keeping it transverse throughout.^[ref] For an illustrative ideal comparison, take $T_1=1\mathrm{s}$, $T_2=0.1\mathrm{s}$ and storage time $T=0.5\mathrm{s}$. The storage-dependent nuclear spin relaxation factors are $e^{-T/T_1}\simeq 0.607$ and $e^{-T/T_2}\simeq 0.00674$. Even allowing the ideal three-pulse pathway's initial factor of $1/2$, the former factor is about 45 times larger. This compares only that storage contribution: pulse losses, the other transverse intervals and diffusion attenuation still matter.^[ref]

Jacob Schaefer was a physical chemistry researcher who developed methods for studying complex solid materials using solid-state nuclear magnetic resonance. After his 1964 doctorate he worked at Monsanto, then joined Washington University in 1986. His contributions included cross-polarization magic-angle spinning with Edward O. Stejskal and rotational-echo double resonance with Terry Gullion.^[ref]

The materials in the 1976 cross-polarization magic-angle spinning demonstration made the method's reach tangible. They included polysulfone, ebony wood and a cylinder cut from an ivory billiard ball. Schaefer's father and grandfather were billiards champions; a familiar object became a specimen for measuring carbon-13 responses in a complex solid. Combining polarization transfer with magic angle spinning made weak and broadened solid-state responses much more accessible.^[ref]

REDOR addresses another measurement problem. Magic angle spinning averages interactions that broaden spectra, but some of those interactions carry structural information. Appropriately timed radio frequency pulses restore sensitivity to NMR dipolar coupling between different nuclear species. Comparing a reference echo with a deliberately dephased echo then probes that coupling, with structural interpretation supplied by a suitable spin model.^[ref]

Schaefer reproduced a laboratory record from 29 May 1987 in which Gullion measured carbon-13 spectra of nitrogen-15-labelled alanine. Carbon remained at natural isotopic abundance. The record compares full and dephased echoes at a carbon frequency of $50.3\mathrm{MHz}$, using magic angle spinning at $3.2\mathrm{kHz}$ and 10 rotor periods of dipolar evolution. The corresponding duration isThe reproduced record does not give sample mass or number of accumulated scans. Later use of XY8 NMR phase cycling suppressed pulse-train amplitude and phase errors, enabling measurements of weaker couplings over longer pulse trains.^[ref]

Derek Jones is a physicist at Cardiff University whose research develops quantitative magnetic resonance imaging, especially diffusion tensor imaging. He trained in physics at Nottingham, medical physics at Leeds and completed a Leicester doctorate on diffusion tensor imaging. His work asks how acquisition design changes what can be inferred from a measured signal.^[ref]

Jones investigated how diffusion MRI gradient sampling affects the measurement uncertainty of inferred diffusion tensors. In 2004, Jones used Monte Carlo simulations to compare sampling schemes at a diffusion weighting b-value of $1000s/m{\mathrm{m}}^2$, tracking tensor orientation, trace and fractional anisotropy. It showed why a minimal set of directions need not give robust estimates; its numerical findings belong to the tested models and noise conditions.^[ref]

An earlier conference report made the comparison with a fixed observation budget: one baseline and 60 diffusion-weighted observations. Six unique orientations repeated 10 times and 30 orientations repeated twice therefore used the same number of diffusion-weighted observations. Varying angular coverage while controlling that budget separates a direction-design question from simply acquiring more data.^[ref]

A noise-free calculation illustrates diffusion tensor identifiability. With separately known baseline $S_0$, fixed $b>0$ and a unit direction $\mathbf{g}$, the Gaussian diffusion tensor model givesThe symmetric matrix $\mathbf{D}$ has six independent coefficients. Its quadratic form produces a row $(g_x^2,g_y^2,g_z^2,2g_x{g}_y,2g_x{g}_z,2g_y{g}_z)$ in a linear least squares design. Directions $\pm {\mathbf{e}}_x,\pm {\mathbf{e}}_y,\pm {\mathbf{e}}_z$ give six observations but only matrix rank three: opposite directions repeat a row and the off-diagonal coefficients remain undetermined.

Adding the normalized mixed directions $({\mathbf{e}}_x+{\mathbf{e}}_y)/\sqrt{2}$, $({\mathbf{e}}_x+{\mathbf{e}}_z)/\sqrt{2}$ and $({\mathbf{e}}_y+{\mathbf{e}}_z)/\sqrt{2}$ to the three positive coordinate axes instead gives matrix rank six. For example,This establishes uniqueness in the stated noise-free model. It does not establish small measurement uncertainty or an optimal experimental design.

Jones also interviewed John E. Tanner about the physical origins of pulsed field gradient NMR. The interview preserved concrete details of the apparatus, including Tanner's carefully spaced mica stack and the practical difficulties of rapidly switching magnetic field gradients.^[ref]

Terry Gullion is a physical chemist whose work develops solid-state nuclear magnetic resonance. With Jacob Schaefer, he developed rotational-echo double resonance, or REDOR, which restores sensitivity to heteronuclear NMR dipolar coupling in a spinning solid. His first-person retrospective describes the method as a way to measure couplings and infer structural information.^[ref][ref]

Institutional profile: www.chemistry.wvu.edu/directory/professors/terry-gullion

The physical problem is that magic angle spinning suppresses interactions that broaden spectra but can also remove useful structural information. REDOR uses controlled pulse timing to reintroduce a selected interaction. A paired acquisition compares a reference signal $S_0$ with a dephased signal $S$ under matched conditions. Varying the evolution time supplies more information than a single intensity difference.^[ref]

For an original arithmetic example, $S_0=100$ and $S=72$ give fractional dephasing $(S_0-S)/S_0=0.28$. This does not directly mean that 28 percent of the atoms occupy a particular state. Structural inference requires an appropriate spin model, evolution times and controls on the acquisition. The example shows the inferential step that Gullion's method makes possible: a controlled change in a spectrum can encode an otherwise hidden interaction.

Lynette Cegelski is a Stanford chemist who develops and applies solid-state nuclear magnetic resonance to determine composition and structure in complex materials. Her work connects the measured spectrum with the quantities that can be inferred from it.^[ref]

In a coauthored 2019 materials study, carbon-13 cross-polarization magic-angle spinning spectra of individual polymer components were compared with spectra of intact polymer materials. The comparison yielded approximate carbon contributions from major components. Measuring the material itself provides information different from estimating its composition only from unused starting components.^[ref]

An original calibration example explains why spectral response matters. Suppose two separately resolved contributions have intensities $I_A=60$ and $I_B=40$, with known spectroscopic response factors $k_A=2$ and $k_B=1$ in a model $I_i=k_i{n}_i$. The inferred carbon counts are proportional to 30 and 40, so the A fraction is $30/70=3/7$, rather than the raw-intensity fraction $60/100$.

These invented coefficients are not results from the paper. They illustrate the distinction between observing a spectral feature and calibrating its contribution to composition. Cegelski's materials measurements exemplify how solid-state nuclear magnetic resonance can make insoluble samples accessible to direct compositional analysis while retaining explicit limits on quantification.

James Keeler works on high-resolution nuclear magnetic resonance methods and explains their physical basis through experiments and mathematical models. His university profile identifies this research focus and his authorship of Understanding NMR Spectroscopy.^[ref] The author-hosted Irvine notes give a particularly concrete account of how receiver electronics turn rotating nuclear magnetization into a signed frequency measurement.^[ref]

A single receiver channel proportional to $\cos (\Omega t)$ cannot distinguish offsets $+\Omega$ and $-\Omega$, because cosine is even. Two receiver references separated in phase by $\pi /2$ give quadrature detection: the two outputs represent $\cos (\Omega t)$ and $\sin (\Omega t)$ and combine into the complex number $e^{i\Omega t}$. This determines the sense of rotation in the rotating frame as well as its rate.^[ref]

For an original numerical illustration, offsets of $+100\mathrm{Hz}$ and $-100\mathrm{Hz}$ at $t=1.25\mathrm{ms}$ have phases $+\pi /4$ and $-\pi /4$. Both give the same real channel $1/\sqrt{2}$, but the imaginary channels are respectively $+1/\sqrt{2}$ and $-1/\sqrt{2}$. This is why retaining both receiver channels preserves information lost by a single real measurement.

Fei Wang is the first author, printed as F. Wang, of the 2016 experimental study of robust dynamical decoupling with finite-strength control pulses. The corresponding 2017 APS abstract identifies Fei Wang and the same five coauthors under the same research title.^[ref]

The experiment controlled an electron-spin qubit at a nitrogen-vacancy center in diamond. A $532\mathrm{nm}$ laser initialized and read out the center through fluorescence; a transmission line delivered microwave control and deliberately injected noise. Comparing pulse sequences tested whether slow, finite-duration pulses could suppress dephasing and relaxation noise, rather than requiring ideal instantaneous rotations. The study found that appropriately arranged slow pulses could approach the performance of strong fast pulses.^[ref]

An original pulse-area example explains the constraint. For resonant control $H_c=\hslash \Omega {\sigma }_x/2$, a constant pulse of duration $t_p$ rotates through $\Omega t_p$. A $\pi$ pulse with $\Omega =2\pi \times 100\mathrm{kHz}$ lasts $5\mu \mathrm{s}$; at $\Omega =2\pi \times 10\mathrm{kHz}$ it lasts $50\mu \mathrm{s}$. Both have the same rotation angle, but the system experiences noise for ten times longer during the second pulse. The demonstrated sequence design addresses that finite-duration problem; pulse area alone does not establish noise cancellation.

Steve R. Domen developed physical water calorimetry methods at the National Institute of Standards and Technology. His 1994 sealed-water instrument measured absorbed dose from a minute radiation-induced temperature rise, while investigating how dissolved gases change the fraction of deposited energy that appears as heat.^[ref]

The apparatus enclosed water in a thin glass vessel immersed in a larger water tank. Two calibrated thermistors in glass capillaries formed part of a Wheatstone bridge that detected the temperature response. The vessel also limited convection. Comparing different dissolved-gas conditions tested the heat defect, rather than assuming that all absorbed energy immediately becomes heat.^[ref]

For an original ideal calculation, neglect the heat defect and heat transfer during a reading. With water specific heat capacity $c_p=4180\mathrm{J}\mathrm{k}{\mathrm{g}}^{-1}{\mathrm{K}}^{-1}$ and measured rise $\Delta T=0.240\mathrm{mK}$,This illustrates why sub-millikelvin thermometry matters. It is not a reported run: the real measurement model must include the instrument's corrections and measurement uncertainty.

Emilio Alfaro-Bou contributed experimental crashworthiness research at NASA Langley, including the use of measured aircraft crash pulses to test energy-absorbing seat structures. The publisher names him in full as the first author of the 1981 paper whose citation abbreviates the name to E. Alfaro-Bou.^[ref]

The study analyzed acceleration histories from twelve light-aircraft crash tests. It then used two vertical drop tests at $12.8\mathrm{m}{\mathrm{s}}^{-1}$ to assess an energy-absorbing seat prototype under a specified impact pulse, comparing instrumented dummy and structural response with a finite element method model.^[ref] The physical question is how a load path changes the acceleration-time history; a static strength measurement alone does not answer it.

For an original ideal pulse comparison, take a rigid test mass initially moving at $12\mathrm{m}{\mathrm{s}}^{-1}$. A constant opposing acceleration of $200\mathrm{m}{\mathrm{s}}^{-2}$ stops it in $0.060\mathrm{s}$ over $0.36\mathrm{m}$. Halving that acceleration to $100\mathrm{m}{\mathrm{s}}^{-2}$ doubles the time to $0.120\mathrm{s}$ and the stopping distance to $0.72\mathrm{m}$:Both pulses remove the same momentum per unit mass, $\int adt=12\mathrm{m}{\mathrm{s}}^{-1}$, but require different deformation strokes. These stipulated constant pulses illustrate the tradeoff; they are not measured histories from the paper.

Francesco D'Angelo is an optical specialist associated with Edmund Optics, whose own laser-optics staff directory identifies him as a Senior Solutions Engineer.^[ref] He is the named author of the technical note Propagation of a Gaussian Beam Through a Thin Lens by Francesco D'Angelo, which explains Gaussian beam propagation and transformation by a thin lens.

The note relates beam waist, beam divergence and Rayleigh range, then uses the complex beam parameter to calculate how a thin lens changes the beam. This connects an optical component specification to the actual position and size of a focused beam, instead of treating every incident beam as a perfectly parallel bundle of rays.^[ref]

An illustrative consequence of the note's ideal Gaussian beam relation $w_0\theta =\lambda /\pi$ is easy to check. At a fixed wavelength $\lambda =1\mu \mathrm{m}$, a beam waist radius of $0.5\mathrm{mm}$ gives a far-field beam divergence half-angle of approximately $0.637\mathrm{mrad}$. Halving the beam waist radius doubles that half-angle. Focusing to a smaller spot and obtaining lower beam divergence cannot be chosen independently within this model.^[ref]

The employer's laser-optics staff directory includes a labeled portrait.

Stefan Meyer, the mass-spectrometry researcher identified by the 2017 paper below, developed automated analysis of time-of-flight mass spectrometry data with collaborators. The paper lists his affiliation with Space Research and Planetary Sciences at the University of Bern. Its motivation includes handling large numbers of measurements for chemical-composition studies in space instrumentation.^[ref]

The analysis connects sampled waveforms to mass-related quantities rather than treating every peak position as a known species. Its instrument calibration model relates the flight time $t$ to mass-to-charge ratio throughwith instrument-dependent constants $k_0$ and $t_0$. Identified isotopes provide reference points for fitting the time-to-mass scale.^[ref]

For an original sensitivity calculation, suppose the corrected flight time is $t-t_0=20\mu \mathrm{s}$ and a timing displacement of $0.02\mu \mathrm{s}$ is introduced while the fitted constants are held fixed. The inferred ratio changes byor $0.2001\%$. A0.1-percent timing change therefore produces about a0.2-percent change in this modeled mass-to-charge value. This is a consequence of the square law, not the paper's measured accuracy for an instrument.

The same study also describes integrating peak areas for quantitative analysis. Converting time to a mass scale, estimating an integrated signal and identifying a species are different analysis tasks; automation must keep their assumptions and reference data explicit.^[ref]

P. Matousek, identified by the Central Laser Facility as Pavel Matousek, developed spatially offset Raman spectroscopy for chemical measurements through diffusely scattering material. His institutional profile also describes work on optical parametric chirped pulse amplification and rejection of fluorescence in Raman spectroscopy.^[ref]

The 2005 team measured a buried trans-Stilbene layer below $1\mathrm{mm}$ of Poly(methyl methacrylate) powder. The reported 19-fold contrast improvement concerned the buried layer's spectral visibility; it did not mean that the sample emitted 19 times as many Raman photons.^[ref]

For an original contrast example, a collection arrangement yielding 100 surface counts and 10 buried-layer counts has a buried-to-surface ratio $0.1$. Another arrangement yielding 10 surface counts and 4 buried-layer counts has ratio $0.4$. The ratio improves fourfold although the buried-layer count decreases. This illustrates why a collection geometry can make chemical identification easier without increasing absolute signal. Whether the second measurement is more precise also depends on noise, collection duration and background.

I. P. Clark coauthored the 2005 spatially offset Raman spectroscopy paper. Its collection geometry changes the mixture of signals arriving from an obscuring surface and the material below it.^[ref]

The Research Complex at Harwell identifies Ian Clark as an Ultra instrument scientist and describes his work on a microbolometer array for measuring the focal size of infrared beams. Knowing a beam's size matters when comparing excitation conditions in time-resolved spectroscopy.^[ref]

For an original Gaussian beam example, suppose the pulse radiant exposure is $F(r)=F_0\exp (-2r^2/w^2)$, with total pulse energy $E$. Integration over the transverse plane gives $E=F_0\pi w^2/2$, so $F_0=2E/(\pi w^2)$. If the actual radius is $110\mu \mathrm{m}$ but the analysis assumes $100\mu \mathrm{m}$, it overestimates peak radiant exposure by $(110/100{)}^2=1.21$, or $21\%$. Measuring pulse energy alone therefore does not determine the excitation delivered per unit area. These values illustrate the dependence on spot size, not a measured error in Clark's apparatus.

E. R. C. Draper coauthored the 2005 demonstration of spatially offset Raman spectroscopy with P. Matousek and colleagues. The method distinguishes contributions from different depths by changing where scattered light is collected relative to the illuminated spot.^[ref]

An original two-layer model makes the separation concrete. Let $S$ and $B$ be fixed surface and buried-layer Raman spectra. Suppose two collection arrangements measure $y_0=3S+B$ and $y_1=S+2B$. The linear combination $3y_1-y_0=5B$ removes the surface spectrum exactly in this ideal model. The result depends on knowing the relative surface coefficients; it is not a claim that real tissue always follows these two numbers.

This example explains why a displaced detector can supply useful information even when a scattering sample prevents a sharp optical image of its interior. The two measurements have different mixture coefficients. Recovering the buried signal depends on that difference and on measurement noise, not solely on collecting more light.

M. D. Morris, or Michael D. Morris, is a chemist whose research connects Raman spectroscopy and chemical imaging with the composition and mechanics of bone and other tissues. His University of Michigan profile describes both instrument development and image processing for spectroscopic contrast.^[ref]

A central idea is to retain a Raman spectrum at each sampled position instead of recording only brightness. A map of a phosphate band can then emphasize mineral, while a different spectral contribution carries information about protein. Morris and W. F. Finney also studied how bone spectra respond during controlled elastic loading.^[ref]

As an original two-channel example, suppose reference responses for mineral and an organic component give measured intensities $I_1=2a+b$ and $I_2=a+3b$. Measurements $(I_1,I_2)=(5,5)$ yield $a=2$ and $b=1$ by solving the linear system. These are model response coefficients, not automatically mass fractions: quantitative composition additionally requires suitable reference specimens and measurement calibration. The example shows why spectral information can separate contributions that a single brightness image mixes.

A. E. Goodship coauthored the 2005 spatially offset Raman spectroscopy paper with E. R. C. Draper, M. D. Morris and the laser-spectroscopy team. The reported buried-layer demonstration used trans-Stilbene beneath a scattering Poly(methyl methacrylate) layer.^[ref]

The experiment's motivation is chemical access through an obscuring surface. It should be distinguished from a direct measurement of material strength: identifying a Raman spectrum beneath a surface does not by itself measure a specimen's Young's modulus or establish that it will resist fracture.

For an original illustration, two hypothetical specimens can have equal mineral-to-organic spectral ratios while one contains a large crack. The ratio records a compositional contrast, whereas crack geometry changes the mechanical load path. Combining Raman spectroscopy with a mechanical test can therefore answer a different question from either measurement alone. This is a general measurement distinction, not an additional experimental result attributed to the 2005 paper.

N. Everall coauthored the 2005 demonstration of spatially offset Raman spectroscopy. By changing collection position, the experiment changed the relative surface and subsurface contributions to a measured Raman spectrum.^[ref]

The result highlights an experimental distinction between removing an unwanted mean signal and removing its fluctuations. In an original idealized example, suppose a measured spectral channel contains 1000 expected surface counts and 100 expected buried-layer counts. Under independent Poisson photon counting, its variance is $1100$. Even if the surface mean of 1000 were known exactly and subtracted, the remaining estimate would still have standard deviation $\sqrt{1100}\approx 33.2$ counts, not $\sqrt{100}=10$ counts.

A surface estimate obtained from a second noisy spectrum adds further uncertainty. Optical collection that changes the mixture before detection can therefore offer something different from subtracting a large background afterward. The hypothetical counts explain a measurement principle; they are not experimental count values attributed to Everall or the 2005 paper.

M. Towrie coauthored the 2005 demonstration of spatially offset Raman spectroscopy. Its Raman spectroscopy measurement varied the lateral collection position to distinguish buried and surface signals.^[ref]

The Central Laser Facility identifies the researcher as Mike Towrie and describes his work in the Ultra group and optical instrumentation. Such apparatus makes time and wavelength controlled experimental variables, rather than recording only a specimen's overall brightness.^[ref]

An original timing example illustrates a constraint in pump-probe spectroscopy. A laser operating at $100\mathrm{kHz}$ sends successive pulses $T=1/f=10\mu \mathrm{s}$ apart. If a sample takes $1\mathrm{ms}$ to recover, approximately 100 pulse intervals fit into that recovery time. Treating every pulse as an independent measurement of an unperturbed sample would then need justification. The numerical sample is hypothetical; the calculation explains why repetition rate, recovery and excitation conditions belong in an experimental description.

W. F. Finney, published in full as William F. Finney, collaborated with M. D. Morris on using Raman spectroscopy to study bone under mechanical loading. Their experiment connected a change in a Raman spectrum to deformation of a living material's mineral component, rather than merely identifying its chemical ingredients.^[ref]

The apparatus held hydrated mouse femora in a mechanical tester on a Raman spectroscopy microprobe stage. A load cell monitored the applied loading, which stayed below yielding, while the experiment followed shifts of a phosphate vibrational band. This joined a mechanical measurement to a molecular-scale probe of the loaded bone.^[ref]

For an original illustration of the mechanical scale, a specimen segment of initial length $10\mathrm{mm}$ that extends by $0.02\mathrm{mm}$ has engineering strain $\epsilon =0.02/10=0.002$, or $0.2\%$. A simultaneous Raman shift measurement could track how a molecular vibration changes during that extension. The numerical extension is illustrative; it is not a reported value from Finney's experiment.