Let \( \overrightarrow { a } ,\overrightarrow { b } \) and \( \overrightarrow { c } \) be three unit vectors such that \( \overrightarrow { a } \times \left( \overrightarrow { b } \times \overrightarrow { c } \right) =\frac { \sqrt { 3 } }{ 2 } \left( \overrightarrow { b } +\overrightarrow { c } \right) \). If \( \overrightarrow { b } \) is not parallel to \( \overrightarrow { c } \), then the angle between \( \overrightarrow { a } \) and \( \overrightarrow { b } \) is:
1
\( \frac { 3\pi }{ 4 } \)
2
\( \frac { \pi }{ 2 } \)
3
\( \frac { 2\pi }{ 3 } \)
4
\( \frac { 5\pi }{ 6 } \)