Tikz-Draw smooth path to form a spectrum peak

Question

I am using tikz to recreate the following image

What I am trying to do is draw an "extended" and "smooth" trapezoidal shape. My code is

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
  %axes
  \draw[very thick] (0,0)--(8,0);
  \draw[very thick] (0,0)--(0,5) coordinate (y);
  \draw (8,0) node[below] {\eng{Energy}};
  \node [draw=none,rotate=90, yshift=0.3cm] at (0,5) {\eng{Counts}};
  %1st peak
  \draw[thick,blue] (7.3,0)--(7,3)--(5,4)--(4.7,0);
  \draw[blue,dashed] (7,0)--(7,3);
  \draw[blue,dashed] (5,4)--(5,0);
  \draw[blue] (7,3) node[above,right] {$4$};
  \draw[blue] (5,4) node[above,left] {$3$};
  \draw[blue] (6,4.5) node[above] {$\delta E$};
  %2nd peak
  \draw[thick,red] (3.3,0) -- (3,2.5) -- (1,3.5) -- (0.7,0);
  \draw[red,dashed] (3,0)--(3,2.5);
  \draw[red,dashed] (1,0)--(1,3.5);
  \draw[red] (3,2.5) node[above,right] {$1$};
  \draw[red] (1,3.5) node[above,left] {$2$};
  \draw[red] (2,4.5) node[above] {$\delta E$};
\end{tikzpicture}
\end{document}

and my output is

What I'd like to do is make the angles 1,2,3,4 smoother. Also I'd like to make a bit smoother-like having a small tail-the red and blue lines that touch the x-axis. How can these be achieved?

Answer 1

I'm not quite sure what you mean with "extend the two perpendicular to the x-axis lines" but at least drawing a smooth line can be achieved with Bezier curves.

On a straight line like (a) -- (b) you can add (multiple) control point(s) x to create a smooth curve with (a) .. controls (x) .. (b)

(Taken from here)

EDIT: Thanks for editing your question :) let me then revise my answer...

Actually there is a "smooth" modifier for plotting. Additionally, I added another coordinate at the end and at the beginning and increased the y-value of the neighboring coordinates:

\draw[thick, green] plot [smooth] coordinates {(3.5,0) (3.3,0.5)  (3,2.5)  (1,3.5) (0.7,0.5) (0.5,0)};

For comparison the answer of Harish Kumar (both overlaid in green), also with two additional nodes to achieve smoothing along the x-axis.

\draw[thick,green, rounded corners=4mm ] (7.7,0) -- (7.3,0)--(7,3)--(5,4)--(4.7,0) -- (4.3,0);

Answer 2

You can use rounded corners:

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
  %axes
  \draw[very thick] (0,0)--(8,0);
  \draw[very thick] (0,0)--(0,5) coordinate (y);
  \draw (8,0) node[below] {Energy};
  \node [draw=none,rotate=90, yshift=0.3cm] at (0,5) {Counts};
  %1st peak
  \draw[thick,blue,rounded corners=4mm] (7.3,0)--(7,3)--(5,4)--(4.7,0);
  \draw[blue,dashed] (7,0)-- node[pos=1.1,above,right] {$4$}(7,2.6);
  \draw[blue,dashed] (5.1,0)-- node[pos=1.1,above,left] {$3$}(5.1,3.7);
  \draw[blue] (6,4.5) node[above] {$δE$};
  %2nd peak
  \draw[thick,red,rounded corners=4mm] (3.3,0) -- (3,2.5) -- (1,3.5) -- (0.7,0);
  \draw[red,dashed] (2.9,0)-- node[pos=1.1,above,right] {$1$}(2.9,2.3);
  \draw[red,dashed] (1.1,0)-- node[pos=1.1,above,left] {$2$}(1.1,3.25);
  \draw[red] (2,4.5) node[above] {$δE$};
\end{tikzpicture}
\end{document}

I have also made some simplifications in the code for nodes 1, 2, 3 and 4.