%
%  dchem.sty   Donald Arseneau       asnd@reg.triumf.ca
%  (under development)  Mar 24, 1998
%
%  To typeset chemical equations, use $\ch ...$ or \chm{...} for in-line 
%  formulas.
%  For displays, use any of \begin{reaction} ... \end{reaction}, 
%  \begin{reaction*} ... \end{reaction*},  \begin{rxnarray} ... 
%  \end{rxnarray}, or \begin{rxnarray*} ... \end{rxnarray*}:
%  these correspond to {equation} {equation*} {eqnarray} and {eqnarray*}.
%  These environments are numbered as equations unless you define 
%  "\thereaction" (to change the formatting of the number but use the 
%  same counter), and/or create the new counter with \newcounter{reaction}, 
%  in which case they are numbered separately.
%  e.g.:  \newcommand\thereaction{R\arabic{reaction}}
%  or     \newcounter{reaction}
%  or, to number separately with a separate format (sensible)
%  \newcounter{reaction}   \renewcommand\thereaction{R\arabic{reaction}}
%
%  Use \ma or \mth ("math") to produce regular math inside chemistry:
%  \begin{reaction}
%    H + O_2 \eqbm^{\ma k\sub{a}}_{\ma k\sub{-a}} HO_2 \qquad \mth{\Delta G}
%  \end{reaction}
%  Use \chemistry and \mathematics like \ch or \ma, but \chemistry also
%  changes the equation numbering to be reaction numbering (if they are 
%  different).  The long-name versions are for math environments that have
%  no chemistry analog, or for long portions of documents, or whole documents.
%
%  See comments below (at ***) for: Labelled arrows, subscripts (\sub), 
%  units (\un), \degree, \excited, \eV.

\@ifundefined{frozen@everymath}{% Old LaTeX; use \everymath
 \newcommand\ch{\fam\z@\everymath{\fam\z@}}% like \rm but don't have to repeat
 \newcommand\chemistry{\ch\everydisplay{\ch}%
   \let\theequation\thereaction \let\c@equation\c@reaction 
   \let\p@equation\p@reaction}% declares all math to be chemistry
 \newcommand\ma{\fam\m@ne\everymath{}}% brings back regular math in chem
 \newcommand\mathematics{\ma\everydisplay{}}% declares normal math
}{% New LaTeX, with subverted \everymath
 \def\dch@ch{\fam\z@}
 \let\dch@everymath\@empty
 \let\dch@everydisp\@empty
% If existing every-math hook is the usual, insert my hook at the best place;
% otherwise, just append my hook.  Then do the same for every-display.
 \def\@tempa{\check@math@fonts\the\everymath}%
 \edef\@tempb{\the\frozen@everymath}%
 \ifx\@tempa\@tempb
  \frozen@everymath{\check@math@fonts\dch@everymath\the\everymath}%
 \else
  \addto@hook\frozen@everymath{\dch@everymath}%
 \fi
 \def\@tempa{\check@math@fonts\the\everydisplay}%
 \edef\@tempb{\the\frozen@everydisplay}%
 \ifx\@tempa\@tempb
  \frozen@everydisplay{\check@math@fonts\dch@everydisp\the\everydisplay}%
 \else
  \addto@hook\frozen@everydisplay{\dch@everydisp}%
 \fi
 \newcommand\ch{\fam\z@\let\dch@everymath\dch@ch}% like \rm
 \newcommand\chemistry{\ch\let\dch@everydisp\ch
   \let\theequation\thereaction \let\c@equation\c@reaction 
   \let\p@equation\p@reaction}% all math to be chemistry
 \newcommand\ma{\fam\m@ne\let\dch@everymath\@empty}% restore regular math 
 \newcommand\mathematics{\ma\let\dch@everydisp\@empty}% declares normal math
}
\newcommand\chm[1]{\begingroup\ensuremath{\ch#1}\endgroup}
\newcommand\mth[1]{\begingroup\ensuremath{\ma#1}\endgroup}

\AtBeginDocument{%
 \@ifundefined{thereaction}{\def\thereaction{\@arabic\c@reaction}}\relax
 \@ifundefined{c@reaction}{\let\c@reaction\c@equation}\relax
 \@ifundefined{p@reaction}{\let\p@reaction\p@equation}\relax
}

\catcode`\*=11 % make * letter for easy definition of * environment
\newcommand\rxnarray{\chemistry \eqnarray}\let\endrxnarray\endeqnarray
\newcommand\rxnarray*{\chemistry \eqnarray*}\let\endrxnarray*\endeqnarray*
\newcommand\reaction{\chemistry \equation}\let\endreaction\endequation
\newcommand\reaction*{\chemistry \displaymath}\let\endreaction*\enddisplaymath
\catcode`\*=12 % make * other again
% 
%-------***
%  Roman subscripts: \sub, for subscript labels like k\sub{H} or k\sub{abs};
%  also give subscript in text: drink H\sub{2}O
%
\def\sub#1{\relax\ifmmode_\bgroup\else$_\bgroup\aftergroup$\fi \ch #1\egroup}
% 
%  ====== Labeled Arrows =======***
%  Chemical relations that take labels above and below.  The labels are typed
%  as superscripts and/or subscripts.  There are two versions of each: the
%  smaller fixed size version (\yields) and the larger one that expands to
%  match its labels (\Yields).  The small versions get smaller in fractions 
%  and subscripts and their labels are the appropriate relative script-size
%  (C-down);  the arrow size is determined only by the current math style,
%  not by its labels.  All the capitalized versions have a default minimum 
%  length of 1.1 cm, but a different length can be specified as an optional 
%  argument (\Eqbm[45pt]^{k_{1}}_{k_{-1}}).  This a *minimum* length and
%  the arrow may get larger to make sure it is longer than its label.  
%  These larger versions are always in display size with labels in 
%  text-style.
%
%  \yields, \Yields   --->
%  \eqbm, \Eqbm       (right-left-harpoons)
%  \forms, \Forms     ===>  % name subject to change!!!
%  \twoway, \Twoway   (both-direction arrows) % name subject to change!!!
%  \madeby, \Madeby   <---  % name subject to change!!!
%  \leftyields, \Leftyields: alternate names for madeby
%  \upyields, \Upyields      (uparrow)
%  \downyields, \Downyields  (downarrow)
%  \udyields, \Udyields      (vertical two-way; there is no vertical eqbm)
%
%  e.g.,  $\ch 4Fe + 3O_2 \yields^{H_2O}_{\triangle} 2Fe_2O_3 $
%

\def\yields{\labeledrel\longrightarrow}
\def\Yields{\Labeledrel\;{\;\,}\rightarrowfill}

\def\forms{\labeledrel\Longrightarrow}
\def\Forms{\Labeledrel\;{\;\,}\Rightarrowfill}

\def\eqbm{\labeledrel{\mathrel{\mathpalette{\protect\rlPOON}{}}}}
\def\Eqbm{\Labeledrel\;\;{\protect\rightleftharpoonsfill}}

\def\twoway{\labeledrel{\mathrel{\mathpalette{\protect\twowaY}{}}}}
\def\Twoway{\Labeledrel\;\;{\protect\twowayarrowsfill}}

\def\madeby{\labeledrel\longleftarrow}
\def\Madeby{\Labeledrel{\;\,}\;\leftarrowfill}
\let\leftyields\madeby
\let\Leftyields\Madeby

% \def\mapsto{\labeledrel{\mapstochar\rightarrow}}
% \def\Mapsto{\Labeledrel\;\;{$\m@th\mapstochar$\rightarrowfill}}

\def\upyields{\Labelledvertic@L\scriptstyle\uparrow.{2\p@}\z@[.8em]}
\def\downyields{\Labelledvertic@L\scriptstyle\downarrow.\z@{2\p@}[.8em]}
\def\udyields{\Labelledvertic@L\scriptstyle
        {\uparrow\kern-3\p@}\downarrow\p@\p@[.8em]}

\def\Upyields{\Labelledvertical\dch@labelsty\uparrow.{5\p@}{2\p@}}
\def\Downyields{\Labelledvertical\dch@labelsty\downarrow.{2\p@}{5\p@}}
\def\Udyields{\Labelledvertical\dch@labelsty
        {\uparrow\kern-3\p@}\downarrow{3.5\p@}{3.5\p@}}

\edef\labeledrel{\protect\csname labeledrel \endcsname}
\@namedef{labeledrel }#1{\mathrel\bgroup\mathop{#1}\limits\t@StSS}
\def\t@StSS{\@ifnextchar^{\aPPscriPt}{\@ifnextchar_{\aPPscriPt}{\egroup}}}
\def\aPPscriPt#1#2{#1{\LR@lf#2\LR@rt}\t@StSS}
\let\LR@lf\relax
\let\LR@rt\relax

\edef\Labeledrel{\protect\csname Labeledrel \endcsname}
\@namedef{Labeledrel }#1#2#3{\mathrel\bgroup 
  \def\LR@lf{\dch@labelsty#1}\def\LR@rt{#2}%
  \@ifnextchar[{\LabeledreL{#3}}{\LabeledreL{#3}[1.1cm]}}
\def\LabeledreL#1[#2]{\mathop{\hbox to#2{#1}}\limits\t@StSS}

\let\dch@labelsty\textstyle % default; see option settings below

\def\Labelledvertical#1#2#3#4#5{\@ifnextchar[%
 {\Labelledvertic@L{#1}{#2\L@bvertvr}{#3}{#4}{#5}}%
 {\Labelledvertic@L{#1}{#2\L@bvertvr}{#3}{#4}{#5}[.8cm]}}

% much simpler would be typing the labels directly around \upyields, but
% that would mean no automatic sizing and no automatic centering.
% #1: style command  #2: vertical arrow command (must have a del-code;
% may be followed by other code to control spacing) #3: additional arrow
% #4: top arrow extension  #5: bottom arrow extension  #6: nominal length
% ^{ }: label on left (box 0)  _{ }: label on right (box 2)
%
\def\Labelledvertic@L#1#2#3#4#5[#6]{\mathrel\bgroup\m@th
 \setbox\z@\null \setbox\tw@\null
 \def\dch@ti{#1}\def\dch@tii{{#2}{#3}{#4}{#5}{#6}}\vt@stSS}
\def\vt@stSS{\@ifnextchar^{\dch@hold\z@}%
  {\@ifnextchar_{\dch@hold\tw@}{\expandafter\L@belv@rt\dch@tii}}}
\def\dch@hold#1#2#3{\setbox#1\hbox{$\dch@ti{#3}$}\vt@stSS}
\def\L@belv@rt#1#2#3#4#5{%
  \ifdim\ht\z@>\ht\tw@ \ht\tw@\ht\z@ \fi % give box 2 the maximum ht and dp
  \ifdim\dp\z@>\dp\tw@ \dp\tw@\dp\z@ \fi
  \ifdim\wd\z@>\wd\tw@ \wd\tw@\wd\z@ \fi % and both boxes the max wd
  \ifdim\wd\tw@>\wd\z@ \setbox\z@\hbox to\wd\tw@{\hfil\unhbox\z@}\fi
  \@tempdimb#3\advance\@tempdimb-#4\divide\@tempdimb\tw@
  \box\z@ %
  \raise\@tempdimb\hbox{$\dch@ti
    \delimiterfactor\@m \delimitershortfall-#3 \advance\delimitershortfall-#4%
    \left#1%
     \vcenter to#5{}%
    \right#2\n@space$}%
  \box\tw@ \egroup}
\def\L@bvertvr{\vrule \@height\ht\tw@ \@depth\dp\tw@ \@width\z@}

\def\rightarrowfill{$\m@th \mathsm@sh{}-\barfill \mathord\rightarrow$}
\def\leftarrowfill{$\m@th \mathord\leftarrow \barfill \mathsm@sh{}-$}

\def\rlPOON#1#2{%  #1=style, #2=unused (required for \mathpalette)
  \dual@bar\p@{\mathsm@sh{#1}-}{#1\leftharpoondown\mkern\NegFourmu}\!%
  \dual@bar\p@{#1\mkern\NegFourmu\rightharpoonup}{\mathsm@sh{#1}-}}

\def\rightleftharpoonsfill{$\m@th
  \dual@bar\p@{\mathsm@sh{}-}{\leftharpoondown\mkern\NegFourmu}%
  \setbox\z@\hbox{\dual@bar\p@{\mkern\NegFourmu-}{-\mkern\NegFourmu}}%
  \ht\z@\z@\dp\z@\z@ \mkern\NegFourmu\cleaders\box\z@\hfill \mkern\NegFourmu
  \dual@bar\p@{\mkern\NegFourmu\rightharpoonup}{\mathsm@sh{}-}$}

% The large separation here and in \twowayarrowsfill is because of 
% Knuth's silly change to CM arrows, giving them fat heads.
\def\twowaY#1#2{%  #1=style, #2=unused (required for \mathpalette)
  \dual@bar{1.7\p@}{\mathsm@sh{#1}-}{#1\leftarrow\mkern\NegFourmu}\!%
  \dual@bar{1.7\p@}{#1\mkern\NegFourmu\rightarrow}{\mathsm@sh{#1}-}}

% ***
% New arrow-fill commands:
% \rightarrowfill, \leftarrowfill (slightly redefined)
% \rightleftharpoonsfill  (for \Eqbm)
% \twowayarrowsfill       (similar, but with full arrow heads)
% \Rightarrowfill, \Leftarrowfill ( ===>  <=== )
% \Leftrightarrowfill   ( <===> )

\def\twowayarrowsfill{$\m@th
  \dual@bar{1.7\p@}{\mathsm@sh{}-}{\leftarrow\mkern\NegFourmu}%
  \setbox\z@\hbox{\dual@bar{1.7\p@}{\mkern\NegFourmu-}{-\mkern\NegFourmu}}%
  \ht\z@\z@\dp\z@\z@ \mkern\NegFourmu\cleaders\box\z@\hfill \mkern\NegFourmu
  \dual@bar{1.7\p@}{\mkern\NegFourmu\rightarrow}{\mathsm@sh{}-}$}

% Macro for my repeating units of two bars, as for \eqbm.
% #1 = 1/2 the separation; #2 = the top "bar"; #3 = the bottom "bar"
\def\dual@bar#1#2#3{\ooalign{\raise#1\hbox{$#2$}\cr
  \lower#1\hbox{$#3$}\cr}}

\def\barfill{\setbox\z@\hbox{$\mkern\NegTwomu\mathord-\mkern\NegTwomu$}%
  \ht\z@\z@\dp\z@\z@ \mkern\NegSevmu\cleaders\copy\z@\hfill\mkern\NegSevmu}

\newmuskip\NegTwomu \NegTwomu=-2mu\relax
\newmuskip\NegFourmu \NegFourmu=-4mu\relax
\newmuskip\NegSevmu \NegSevmu=-7mu\relax

\def\Rightarrowfill{$\m@th\mathord=\mkern\NegSevmu%
  \cleaders\hbox{$\mkern\NegTwomu\mathord=\mkern\NegTwomu$}\hfill
  \mkern\NegSevmu\mathord\Rightarrow$}

\def\Leftarrowfill{$\m@th\mathord\Leftarrow\mkern\NegSevmu%
  \cleaders\hbox{$\mkern\NegTwomu\mathord=\mkern\NegTwomu$}\hfill
  \mkern\NegSevmu\mathord=$}

\def\Leftrightarrowfill{$\m@th\mathord\Leftarrow\mkern\NegSevmu%
  \cleaders\hbox{$\mkern\NegTwomu\mathord=\mkern\NegTwomu$}\hfill
  \mkern\NegSevmu\mathord\Rightarrow$}

% Handle amsmath redefinition of \smash internals ... Grrrrr!
\def\smash@{tb}

%***
%  \un   Put units after a number; e.g., 0.0821\un{l\,atm\,mol^{-1}\,K^{-1}}
%        Use \, or space to put thin spaces between units.  Works in math and
%        text mode. \un is fragile.
%
\newmuskip\unitmuskip \unitmuskip=3mu plus 1mu minus 1mu
\def\unitmskip{\penalty\@highpenalty \mskip\unitmuskip}
\def\unithskip{\leavevmode \penalty\@highpenalty
 \hskip.22em plus.13em minus.1em}
\newcommand\un[1]{\leavevmode\unskip\penalty\@highpenalty
 \ensuremath{\mskip\medmuskip
 \begingroup \fam\z@ % limit \fam but not style changes
 \let\,\unitmskip \unit@PreserveSpaces\@empty #1 \unit@PreserveSpaces
 \endgroup}}
\def\unit@PreserveSpaces#1 {#1\@ifnextchar\unit@PreserveSpaces{\@gobble}%
 {\unitmskip \unit@PreserveSpaces\@empty}}
%

% ***
% Some symbols and text.
%
% \degree  - superscript circle
% \eV      - kerned roman eV
% \excited - superscipt full-size * (math or text)
% \saturn  - circle with bar through it
% 
\newcommand\degree{\relax\ifmmode^\circ\else $^\circ$\fi}
\newcommand\excited{\relax \ifmmode^{\textstyle *}\else*\fi}
\newcommand\eV{\mbox{e\kern-.05emV}}
\newcommand\saturn{\mathpalette\@barred\circ}
\def\@barred#1#2{\ooalign{\hfil$#1-$\hfil\cr\hfil$#1#2$\hfil\cr}}

% *** 
% Tags for "structured markup" of miscellaneous notations.  Alternative
% definitions in document preamble can change output style without changing 
% the main document.

% \stst   - standard state.  Default is superscript circle; others shown are
%           superscipt 0 and superscript circle with bar through it.
\newcommand\stst{\degree}
% alternate: \renewcommand\stst{^0}
% alternate: \renewcommand\stst{^{\protect\saturn}}
%
% \ts     - transition state.  Default is superscript double dagger; variants
%           are asterisk, dagger, plus sign, and not-equals
% Should these be split into two or more classes with distinct meanings?
\newcommand\ts{^{\ddagger}}
% \renewcommand\ts{^{\textstyle *}}
% \renewcommand\ts{^{\dagger}}
% \renewcommand\ts{^{+}}
% \renewcommand\ts{^{\neq}}

% *** 
% Tags for "structured markup" of physical state notations.  Alternative
% definitions can change output style without changing the document.
\newcommand{\aq}{(\mkern-1mu\mathit{aq})}
\newcommand{\liq}{(\mkern-.5mu\mathit{l})}
\newcommand{\gas}{(\mathit{g})}
\newcommand{\sol}{(\mkern-.5mu\mathit{s})}
%
% Alternative versions -- roman subscripts 
% \newcommand{\aq}{\sub{aq}}
% \newcommand{\liq}{\sub{\ell}}
% \newcommand{\gas}{\sub{g}}
% \newcommand{\sol}{\sub{s}}

% ***
% Tags for bonds, lone pairs, and unpaired electrons.  Many of these --
% the ones printed above or below the chemical symbol -- must be typed
% before the symbol, and take the symbol as an argument; others are
% just symbols typed where they appear.  Bond lines are *not* provided at
% different sizes for subscripts etc (no "\mathpalette") because they
% shouldn't be used there and doing so would quadruple the execution time.
%
% Bonds for making very simple structures (perhaps using {array}):
% \bond   -  horizontal line; darker and longer than -.
% \vbond  -  vertical bond
% \dbond  -  double \bond
% \tbond  -  tripe \bond
% \dvbond -  double \vbond
% 
% the sizes are parameterized by:
\def\BondWidth{0.4pt}
\def\BondLength{0.7em}
%

\newcommand\bond{\dch@bond\@bond}
\newcommand\dbond{\dch@bond{\@bond\kern.35ex\@bond}}
\newcommand\tbond{\dch@bond{\@bond\kern.25ex\@bond\kern.25ex\@bond}}
\newcommand\vbond{\vcenter{\hrule \@height\BondLength \@width\BondWidth}}
\newcommand\dvbond{{\vbond \kern.35ex\vbond}}
\def\@bond{\hrule \@height\BondWidth \@width\BondLength}
\def\dch@bond#1{\mkern\@ne mu\vcenter{#1}\mkern\@ne mu}

% ***
% Unpaired or paired electrons.  These don't look very good because the 
% positioning is lousy and the separation of double dots is inconsistent.
%                           in-line      above
% lone electron             {\cdot}      \dot{X}
% Pair of electrons         {:}          \ddot{X}
% 
% I should probably define commands for these things in the hope of making
% better output.  Would people actually use more verbose commands??

\newcommand\MathSubscripts{}
\newcommand\ChemSubscripts{}

\@ifundefined{DeclareOption}{\endinput}{}
\let\dch@scr@hook\relax

\ProvidesPackage{dchem}[1998/03/24 test]
\DeclareOption{largelabels}{\let\dch@labelsty\textstyle}
\DeclareOption{smalllabels}{\let\dch@labelsty\scriptstyle}
\DeclareOption{lowersubs}{\let\dch@scr@hook\@empty}
\DeclareOption{eqbmarrows}{\let\eqbm\twoway \let\Eqbm\Twoway}
\ProcessOptions

% ***
% Subscript and superscript positions are adjusted so that subscripts 
% stay at the same height regardless of whether there is a superscipt 
% + or -.  Since this positioning applies to both chemistry and math
% typesetting, it is *not* enabled by default but requires the option
% [lowersubs] or the command \ChemSubscripts.  The default positioning
% can be restored with a \MathSubscripts command.
%
% Set the fontdimen parameters for subscript and superscript position
% so that C_2H_5^+ has both subscripts at the same vertical position.
% Do this by actually comparing H_2 with H_2^+ and adjusting the font's
% sub-lowering (16, 17) by half the difference and setting the super-
% raising (13, 14, 15) to the matching position.  The settings (for
% all three fonts t,s,ss) are determined once per text-font-size and 
% stored in the macro \dch@sizet<size> (e.g. \csname dch@sizet12\endcsname).
% Since some specific fonts are used in different roles at different
% text-font-sizes, the original (dvi) settings for each particular font
% are saved in a macro \dch@size<size> (no "t") before they are changed 
% for the first time.  When that font appears in a different role for 
% another text-font size, those original settings are restored first 
% before making changes.
%
% This procedure sets the positioning each time the font size is changed,
% but, although it keeps a record of the original parameters, the settings
% are not restored for regular math.  Two reasons:
% 1) Having a separate set of values for math and chemistry would mean
%    you couldn't mix math symbols in with chemistry (no K_{\ch H_2O}
%    or \yields^{\ma k_a}).  
% 2) I *like* the modified settings for regular math; I find the regular
%    subscripts too high often.  Though tastes may vary. 
% If you do not select the subscript-alignment option, it is still 
% reasonably easy to avoid ragged placement for the occasional ionic 
% species as $\ch H_2PO_4{}^{-}$.  
%

\@ifundefined{every@math@size}{\endinput}{}
\addto@hook\every@math@size{\dch@scr@hook}

\def\dch@scr@adjust{\@ifundefined{dch@sizet\f@size}%
  {\expandafter\dch@set@script\csname dch@sizet\f@size\endcsname}%
  {\csname dch@sizet\f@size\endcsname}}

% textfont done last so it takes precedence in case it is the same as 
% another style (like at \tiny)
% #1 = single-token command name for executing settings
\def\dch@set@script#1{\begingroup % fontdimen settings are global anyway
% \edef\mymes{Defining settings for size \f@size/\sf@size/\ssf@size.}\show\mymes
  \frozen@everymath{}% Prevent recursion!
  \let#1\@empty \let\dch@do@one\relax
  \dch@set@one\scriptscriptstyle\scriptscriptfont#1\ssf@size
  \dch@set@one\scriptstyle\scriptfont#1\sf@size
  \dch@set@one\textstyle\textfont#1\f@size
  \endgroup #1} % 

\def\dch@set@one#1#2#3#4{%
  \@ifundefined{dch@size#4}%
   {\expandafter\xdef\csname dch@size#4\endcsname{%
      \fontdimen13\the#2\tw@=\the\fontdimen13#2\tw@
      \fontdimen14\the#2\tw@=\the\fontdimen14#2\tw@
      \fontdimen15\the#2\tw@=\the\fontdimen15#2\tw@
      \fontdimen16\the#2\tw@=\the\fontdimen16#2\tw@
      \fontdimen17\the#2\tw@=\the\fontdimen17#2\tw@}%
  }{\csname dch@size#4\endcsname}%
  \setbox\z@\hbox{$#1H_2$}\@tempdima\dp\z@
  \setbox\z@\hbox{$#1H_2^{+\vrule \@height 1em}$}%
%  \message{Depth null: \the\@tempdima, Depth plus: \the\dp\z@, 
%  Height plus: \the\ht\z@. }%
   \ifdim\@tempdima<\dp\z@
%     \message{Original: ^^J
%      \fontdimen13#2\tw@=\the\fontdimen13#2\tw@, 
%      \fontdimen14#2\tw@=\the\fontdimen14#2\tw@,
%      \fontdimen15#2\tw@=\the\fontdimen15#2\tw@,
%      \fontdimen16#2\tw@=\the\fontdimen16#2\tw@,
%      \fontdimen17#2\tw@=\the\fontdimen17#2\tw@. }%
    \advance\@tempdima\dp\z@ \divide\@tempdima\tw@ % new sub lowering
    \@tempdimb\dp\z@ \advance\@tempdimb-\@tempdima % adjustment
%     \message{Adjustment: \the\@tempdimb. }%
    \advance\@tempdimb\ht\z@ \advance\@tempdimb-1em % new super raising
%     \message{Super position: \the\@tempdimb, Sub position: \the\@tempdima. }%
    \xdef#3{#3\dch@do@one#2{\the\@tempdimb}{\the\@tempdima}}%
  \fi} 

\def\dch@do@one#1#2#3{\fontdimen13#1\tw@#2\relax
  \fontdimen14#1\tw@\fontdimen13#1\tw@ \fontdimen15#1\tw@\fontdimen13#1\tw@
  \fontdimen\sixt@@n#1\tw@#3\fontdimen17#1\tw@\fontdimen\sixt@@n#1\tw@}%

\def\MathSubscripts{\let\dch@scr@hook\relax
  \ifx\glb@currsize\f@size  
    \csname dch@size\ssf@size\endcsname
    \csname dch@size\sf@size\endcsname
    \csname dch@size\f@size\endcsname 
  \fi }

\def\ChemSubscripts{\let\dch@scr@hook\dch@scr@adjust 
  \ifx\glb@currsize\f@size \dch@scr@adjust \fi}

\ifx\dch@scr@hook\@empty \let\dch@scr@hook\dch@scr@adjust \fi