What prompted Carter's actions had more to do with his human rights policy than any offer of bribes. If you recall, we had thousands of Iranian students in the US demonstrating in front of the WH with bags over their heads calling for the removal of the Shah and more human rights in Iran. At the time, there were over 50,000 Iranian students in the US, more than any other country in the world.
Carter believed that human rights should be the most important factor driving our foreign policy. He dismissed "real politic" as being unreprsentative of this country even if our national interests were at stake. In a word, Carter was dangerously naive.
The stakes in Iran were high. Iran was a major ally in the region. It had oil, lots of opportunties for American businesses and for the sale of American weapons. The Shah was pro-American. There was even an Israeli trade mission in Tehran. We had over 1,000 official Americans in Iran in 1978, including those along the Caspian monitoring Soviet nuclear tests. Iran was critical to US national interests, but Carter was so involved in the Camp David Peace Accords that he wasn't paying attention to what was happening in Iran.
Carter and Vance believed that they could ease the Shah out and deal with the new democratic government that replaced him. They did not understand the power of the mullahs and their ability to hijack the Revolution. So the unintended consequence was clearing the way for Khomeini to take power. And human rights under Khomeini and subsequently are far worse than under the Shah. And the cruelest cut of all has been Iran's initiation and funding of militant Islamic fundamentalism around the globe, which has killed many Americans. A nuclear armed Iran presents a real danger for the region and us.
Our policy should be regime change. Instead, Obama has been legitimizing the current regime by offering to deal with it. Obama now has a golden opportunity to send a signal to the Iranian opposition that we support their struggle. I doubt he will do that preferring to negotiate with the current regime.