Please list all the years in which the car model Chevrolet Impala was introduced in the market.
year refers to model_year; Chevrolet Impala refers to car_name = 'chevrolet impala'
SELECT DISTINCT T1.model_year FROM production AS T1 INNER JOIN data AS T2 ON T1.ID = T2.ID WHERE T2.car_name = 'chevrolet impala'