“I am well aware that we face many long days and difficult obstacles have to be overcome before we can really see victory,” Ethel Rosenberg wrote while behind bars in 1952, “but I’m still confident that we’ll win our freedom.” Of course, she and husband Julius , convicted in 1951 of conspiracy to commit espionage, did not win their freedom, and a year later they were executed in the electric chair. Some of the couple’s final correspondence is the subject of a new exhibit and website, “Love-Conscience-Conviction: The Rosenberg Case,” at Boston University’s Howard Gotlieb Archival Research Center. It opened Tuesday with a panel discussion that included the Rosenbergs’ sons, Michael and Robert Meeropol, who donated the letters, as well as journalists and authors Jonathan Alter and Stephen Kinzer, former CIA officer Joseph Wippl, and Cold War historian Igor Lukes. “For me, the letters are a real gear shift,” Robert Meeropol, 67, said in an interview before the event. “It’s not the Rosenberg case, it’s Ethel and Julius Rosenberg. For getting to know them as people, the letters are the best window we have.” The website devoted to the Julius and Ethel Rosenberg Archive will include high-resolution images of the more than 500 letters written between Julius and Ethel Rosenberg during their incarceration.