['A', 'pioneering', 'theoretical', 'paper', 'of', 'Martin', 'and', 'Davidson', 'published', 'in', '1978', 'showed', 'that', 'the', 'obtuse', 'isosceles', 'geometry', 'is', 'lower', 'in', 'energy', 'than', 'the', 'linear', 'conformation', '[', '6', ']', '.']