Physical properties - Nitric oxide is a colorless gas with the formula NO. - It is one of the principal oxides of nitrogen. - Nitric oxide is a free radical with an unpaired electron. - It is a heteronuclear diatomic molecule. - Nitric oxide forms in combustion systems and can be generated by lightning in thunderstorms. - The ground state electronic configuration of NO is (1σ)^2(2σ)^2(3σ)^2(4σ*)^2(5σ)^2(1π)^4(2π*)^1. - The first two orbitals are pure atomic 1 and 1 from oxygen and nitrogen respectively. - Orbitals noted with an asterisk are antibonding. - The lone electron in the 2π orbital makes NO a doublet (X ²Π) in its ground state. - The degeneracy of the doublet is split in the fine structure. - The dipole of NO is measured experimentally to be 0.15740 D. - The dipole is oriented from O to N(⁻NO⁺) due to the transfer of negative electronic charge. - Oxygen transfers electronic charge to nitrogen.

Reactions - Upon condensing to a liquid, nitric oxide dimerizes to dinitrogen dioxide. - The association between NO molecules is weak and reversible. - NO can be decomposed to the elements. - Nitric oxide converts into nitrogen dioxide when exposed to oxygen. - This reaction is thought to occur via intermediates like ONOO and ONOONO. - Nitric oxide reacts with transition metals to give complexes called metal nitrosyls. - The most common bonding mode of nitric oxide is the terminal linear type (M−NO). - Nitric oxide can also serve as a one-electron pseudohalide. - The M−N−O group in nitric oxide complexes is characterised by an angle between 120° and 140°. - Nitric oxide can bridge between metal centers through the nitrogen atom in various geometries.

Occupational safety and health - The legal limit for nitric oxide exposure in the workplace is set at 25ppm (30mg/m³) over an 8-hour workday by OSHA. - NIOSH recommends an exposure limit of 25ppm (30mg/m³) over an 8-hour workday. - Nitric oxide is immediately dangerous to life and health at levels of 100ppm. - Occupational exposure to nitric oxide can lead to respiratory issues and lung damage. - Proper ventilation and personal protective equipment should be used to minimize exposure to nitric oxide in the workplace.

Explosion hazard - Liquid nitrogen oxide is highly sensitive to detonation, even without fuel, and can be as explosive as nitroglycerin. - Detonation of liquid nitric oxide near its boiling point (-152°C) can generate a 100 kbar pulse and cause equipment fragmentation. - Nitric oxide is the simplest molecule capable of detonation in all three phases (gas, liquid, and solid). - Industrial accidents have occurred due to the explosion of liquid nitric oxide during distillation. - Gaseous nitric oxide has a detonation velocity of about 2300 m/s, while as a solid, it can reach a velocity of 6100 m/s.

Nobel Prize and research - The Nobel Prize in Physiology or Medicine was awarded in 1998 for the discovery of the role of nitric oxide as a signaling molecule in the cardiovascular system. - Research on nitric oxide donors and their development is an active area of study in pharmacology and medicine. - Nitric oxide has been studied for its potential therapeutic applications, including its role in regulating blood pressure and as a vasodilator. - Scientists have investigated the use of fluorescent indicators to detect and image nitric oxide in biological systems. - The interaction between nitric oxide and other signaling molecules, such as hydrogen sulfide, is an area of ongoing research.