{'fraction_non_alphanumeric': 0.049132947976878616, 'fraction_numerical': 0.007707129094412331, 'mean_word_length': 4.804469273743017, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Evidence of blue-shifting N–H⋯N hydrogen bonding despite elongation of the N–H bond

In most cases of X–H⋯Y hydrogen bonding (X is an electronegative atom and Y is any electron-rich center), the X–H bond gets elongated and the stretching frequency of X–H (νX–H) gets red-shifted. Relatively fewer cases of blue-shifting H-bonding are also known, where the X–H bond contracts leading to an increase in νX–H. Here is presented the first experimental report of blue-shifting N–H⋯N H-bonding that accompanies an increase in N–H bond length as evident from quantum chemistry computations. Pyrrole and N2 have been shown to form N–H⋯N hydrogen bond in an ‘annealed’ N2 matrix, where both doped (pyrrole) and dopant (nitrogen) molecules had scope to align themselves and form stable H-bonded clusters. The infrared spectrum of the annealed matrix shows a blue shift of νN–H by 7 cm−1. Computation of anharmonic frequencies at the MP2/6-31+G(d) level of theory reflects the observed blue shift despite N–H bond lengthening after H-bond formation.