The drastic evolution of molecular systems exposed to ultrashort intense X-ray pulse is a fundamental obstacle for single-particle imaging (SPI) by means of X-ray free electron lasers (XFEL). Here we tackle the simplest molecule H2+ and its diffraction pattern degradations in the strong ultrashort X-ray beam. The semiclassical method of the problem solution and its advantages are described in detail. We apply the method to calculate the electron density autocorrelation functions (ACF) for a few internuclear distances and then discuss numeric simulation data.