= Kyungwon Kwak
{c}
\b[Kyungwon Kwak] is a chemist working on ultrafast <time-resolved spectroscopy> of molecular systems. The Institute for Basic Science directory identifies his Korea University chemistry affiliation, Stanford doctorate and research in molecular dynamics. The primary 2007 paper gives the same full byline.<Kyungwon Kwak profile at the Institute for Basic Science>[People search, Kwak, Kyungwon, Information and Research interests]{ref}
<Kyungwon Kwak>, <Sungnam Park>, <Ilya J. Finkelstein> and <Michael D. Fayer> coauthored the <2D IR center-line slope> method. Their paper defines its slope convention through maxima of frequency-axis slices; that convention matters when converting a plotted geometric slope into a dynamical observable.<Frequency-frequency correlation functions and apodization in two-dimensional infrared vibrational echo spectroscopy: A new approach by Kyungwon Kwak and others>[§II.B, center-line definition]{ref}
An original <bivariate normal distribution> gives a transparent geometric example. Let $x$ be a centered, scaled horizontal frequency and $y$ a centered, scaled vertical frequency. For $|\rho|<1$, take a positive model band
$$
S(x,y)\propto\exp\!\left[-\frac{x^2-2\rho xy+y^2}{2(1-\rho^2)}\right].
$$
At each fixed $y$, maximize over $x$. Differentiating the exponent gives $x=\rho y$. If $\rho=1/2$, the line of maxima has geometric slope $dy/dx=2$, while its inverse is $1/2$. If $\rho=0$, the maxima lie on the vertical line $x=0$: the geometric slope is unbounded, while the inverse tends to zero. Exchanging axes changes which quantity is called the slope.
This model explains an axis convention; it is not a derivation of the full nonlinear optical response. A measured spectrum can contain homogeneous broadening, overlapping bands, finite-pulse effects and noise. Its fitted line need not be the correlation coefficient of a Gaussian probability distribution. The <vibrational frequency-frequency correlation function> requires the spectroscopic model that connects molecular fluctuations with the measured band.
The contribution also addresses <interferogram apodization>: multiplying time-domain data by a <window function> before the <Fourier transform>. The paper's stated symmetry and axis restrictions are essential, rather than a guarantee that arbitrary filtering preserves molecular information.<Frequency-frequency correlation functions and apodization in two-dimensional infrared vibrational echo spectroscopy: A new approach by Kyungwon Kwak and others>[Abstract and Introduction, symmetric apodization along the selected axis]{ref} Useful processing must retain the observable being interpreted, not merely make the image look smoother.
\Image[https://cmsd.ibs.re.kr/img/cmsd_en/contents/2023/02/20230217_041147_30614.jpg]
{title=<Kyungwon Kwak>, portrait explicitly named on the Institute for Basic Science center's Steering Committee page}
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