\documentclass{article}

\usepackage[utf8]{inputenc}
\usepackage{aeguill}
\usepackage{amsmath}

\usepackage{tikz}
\usetikzlibrary{arrows,patterns}

\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{0pt}

\pagestyle{empty}

\begin{document}

\begin{tikzpicture}[>=latex,line width=0.9,
	zeronode/.style={inner sep=0,line width=0,minimum size=0}
]
	% Solid surface
	\begin{scope}[line width=0.5,draw=gray!25]
		\draw[pattern=north west lines,pattern color=gray!25] 
			(0.75,0) -- (-0.75,-1.5) -- (-0.75,1) -- (0.75,2.5) -- (0.75,0);
		\draw (-0.75,-1.5) -- (-1.5,-1.5);
		\draw (-0.75,1) -- (-1.5,1);
		\draw (0.75,2.5) -- (0,2.5);
		\node[zeronode,below] at (-0.75,2) {\scriptsize $Al$ surface};
	\end{scope}
	
	% Coordinate system
	\begin{scope}[->,line width=0.5]
		\draw[->] (0,0) to (0,1)			node (x) [left]		{$\scriptstyle x$};
		\draw[->] (0,0) to (-0.35,-0.35)	node (y) [left]		{$\scriptstyle y$};
		\draw[->] (0,0) to (4.5,0)			node (z) [below] 	{$\scriptstyle z$};
	\end{scope}
	
	% Molecule
	\draw[rotate around={45:(3,0)}]		(2.5,0) -- (3.5,0);
	\draw[fill,rotate around={45:(3,0)}]	(2.5,0) circle (0.05);
	\draw[fill,rotate around={45:(3,0)}]	(3.5,0) circle (0.05);
	\node[zeronode,below] at (3,-0.85) {\scriptsize $N_2$ Molecule};
	\draw[line width=0.5,dashed] (3,0) circle (0.65);
	
	% Velocity
	\node[zeronode] (1) at (2,0.25)	{};
	\node[zeronode] (2) at (1,0.25)	{};
	\draw[->] (1) to node [above] {$\scriptstyle v$} (2);
	
	% Center vector
	\node[zeronode] (0) at (0,0)	{};
	\node[zeronode] (R) at (3,0)	{};
	\draw[->] (0) to node [below] {$\scriptstyle \vec{R}(t)$} (R);
	
	% Angle
	\begin{scope}[line width=0.5]
		\draw (3,0) -- (3,0.5);
		\draw (3,0.5) arc (90:45:0.5);
		\draw[xshift=3cm] (67.5:0.35cm) node {$\scriptstyle\alpha$};
	\end{scope}
	
	% Bond length
	\draw[rotate around={45:(3,0)},<->,line width=0.5] (2.5,-0.2) to node[zeronode,inner sep=1,auto,swap] {$\scriptstyle \varrho$} (3.5,-0.2);
\end{tikzpicture}

\end{document}