Infrared data plot

% This is a 'standalone' plot, so uses the standalone class
\documentclass[border=5pt]{standalone}
% A bit of font set-up: use Latin Modern and T1 encoding
\usepackage[T1]{fontenc}
\usepackage{lmodern}
 
% For typesetting units
\usepackage{siunitx}
 
% Making plots, so load the pgfplots package of course!
\usepackage{pgfplots}
 
% Use the latest settings, so we don't get trapped with old bugs or
% limited features.
\pgfplotsset{compat = newest}
 
% A short list of colours which run from pure blue to pure red:
% eleven steps which is about right for this typo of plot.
\pgfplotscreateplotcyclelist{blue to red}{%
  color=blue\\%
  color=red!10!blue\\%
  color=red!20!blue\\%
  color=red!30!blue\\%
  color=red!40!blue\\%
  color=red!50!blue\\%
  color=red!60!blue\\%
  color=red!70!blue\\%
  color=red!80!blue\\%
  color=red!90!blue\\%
  color=red\\%
}
 
% Turn off the default comma separator for larger numbers
\pgfkeys{
  /pgf/number format/set thousands separator =
}
 
% Create a couple of style to allow control of the settings.
% First, create some very general settings for infra-red data.
% Then, use that and additional settings to specify what happens
% for a difference plot such as this one.
\pgfplotsset{
  infra-red/.style =
    {
      % Chemists always plot infra-red data with the x-axis 'backward'.
      % Physicists work the other way: using a setting here makes it easy
      % to flip things round.
      x dir  = reverse,
      % The labels apply to all plots of this type.
      xlabel = $\tilde{\nu}/\si{\per\cm}$,
      ylabel = $\mathrm{Milliabsorbance}$,
    },
  infra-red difference/.style =
    {
      % The settings here inherit from the more general infra-red plot.
      infra-red,
      % Use the 'controlled' colour change.
      cycle list name     = blue to red,
      % For difference plots, a line showing the zero is useful. This
      % is done by making an additinal grid line.
      extra y ticks       = 0,
      extra y tick labels = \empty,
      extra y tick style  = { grid = major },
      % Since this is a difference, the y-axis needs a modified label.
      ylabel              = $\Delta \mathrm{Milliabsorbance}$,
    }
}
 
% Not everyone likes the 'axis box' effect, which can be turned off by
% uncommenting these two lines. As such a change should (probably) apply to all
% of the plots in a document, this is not tied to a particular plot style.
\pgfplotsset{
%  axis x line* = bottom ,
%  axis y line* = left
}
 
\begin{document}
\begin{tikzpicture}
  \begin{axis}%
    [
      % Choose the general settings
      infra-red difference,
      % Specify the x range
      xmax = 2100,
      xmin = 1800,
      % Set the maximum y value: this is needed for the labels that will be
      % added below.
      ymax = 3
    ]
    % Use a \foreach to seleect data from the raw experimental data:
    % this makes it easy to plot only some of the lines.
    \foreach \yindex in {2,3,...,11}
      \addplot table[y index = \yindex] {\jobname.txt};
    % Adding labels to the peaks: as the text and the horizontal positions
    % are the same, this can be automated. Notice that \foreach does not
    % work here!
    \pgfplotsinvokeforeach{1900,1948,1989,2031}%
      {
        % Each label is done as a 'pin' with the text rotated so it is 
        % vertical. The height has to be set by hand (it's "1.3" here), and
        % to make sure the labels actually show up the ymax key was set
        % earlier, again using hand adjustment.
        \node[coordinate, pin = {[rotate=90]right:#1}] at 
          (axis cs:#1,1.3) { };
      }  
  \end{axis}
\end{tikzpicture}
\end{document}