\begin{table}%t2
\caption{Assigned feature carriers of the IR residue spectrum of the standard, Exp.~OR1.}
\label{idIR}
%\centering
\par
\begin{tabular}{cccc}   \hline \hline  
Feature label & Position  & Carrier & Vibration mode \\ 
              & cm$^{-1}$ &          \\  \hline  
a              & 3500--2300 & R--COOH, alcohols, NH$_4^+$ & OH str., NH str. \\
b             & 3165      & NH$_4^+$$^a$ & ${\nu}_1$+${\nu}_5$$^a$\\
c             & 3035      & NH$_{4}^{+}$$^a$ & ${\nu}_2$+${\nu}_4$\\
d             & 2926      & HMT$^b$ & 2${\nu}_{19}$, ${\nu}_2 + {\nu}_{19}$ \\
e             & 2876      & HMT$^b$, NH$_{4}^{+}$$^a$ & ${\nu}_{18}$ sym. CH$_2$ str., 2${\nu}_4$ of NH$_{4}^{+}$$^a$  \\
f             & 1742      & Esters & C=O str. \\
g             & 1680      & Amides & C=O str. \\ 
h             & 1586      & COO$^-$ in carboxylic acid salts & COO$^-$ antisym. str. \\
i             & 1463      & NH$_{4}^{+}$$^a$ & ${\nu}_4$$^a$ \\ 
j             & 1375      & HMT$^b$ & CH scissoring $^a$ \\
k             & 1320      & COO$^-$ in carboxylic acid salts & COO$^-$ sym. str. \\
l             & 1236      & HMT$^b$ & ${\nu}_{21}$ CN str. \\
m             & 1085      & HOCH$_2$COO$^-$ \\ 
n             & 1007      & HMT$^b$ & ${\nu}_{22}$ CN str.\\
o             & ~918      & carboxylic acid dimers & OH def. \\    
p             & ~820      & HMT$^b$ & NH$_2$ wag \\
q             & ~765      & Ammonium formate? & \\
r             & ~678      & HMT$^b$, ammonium glycolate & ${\nu}_{24}$ CNC def. (for HMT) \\
\hline
\multicolumn{4}{l}{$^a$ Wagner \& Hornig (\cite{Wag50});
$^b$ Bernstein et~al. (\cite{Ber95}).}
\end{tabular}
\end{table}